[gtkmm] Update links to gdkkeysyms.h in the documentation

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 9b58b8466102fa4919c70f2bfc858e2b4b8fe09e
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Wed Jul 13 11:08:17 2022 +0200

    Update links to gdkkeysyms.h in the documentation
    
    The default branch name in gtk's git repo is main (was master).

 gdk/src/event.hg              | 2 +-
 gtk/gtkmm/accelerator.h       | 2 +-
 gtk/gtkmm/accelkey.h          | 2 +-
 gtk/src/cellrendereraccel.hg  | 2 +-
 gtk/src/eventcontrollerkey.hg | 2 +-
 gtk/src/label.hg              | 2 +-
 gtk/src/shortcuttrigger.hg    | 4 ++--
 7 files changed, 8 insertions(+), 8 deletions(-)
---
diff --git a/gdk/src/event.hg b/gdk/src/event.hg
index 4f5cfac3..dc05f99d 100644
--- a/gdk/src/event.hg
+++ b/gdk/src/event.hg
@@ -59,7 +59,7 @@ struct EventSequence;
  *
  * Key values are the codes which are sent whenever a key is pressed or released.
  * The complete list of key values can be found in the
- * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/master/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
+ * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/main/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
  * header file. They are prefixed with <tt>GDK_KEY_</tt>.
  */
 class GDKMM_API Event final
diff --git a/gtk/gtkmm/accelerator.h b/gtk/gtkmm/accelerator.h
index 281e92e0..38c765b5 100644
--- a/gtk/gtkmm/accelerator.h
+++ b/gtk/gtkmm/accelerator.h
@@ -38,7 +38,7 @@ namespace Gtk
  *
  * Key values are the codes which are sent whenever a key is pressed or released.
  * The complete list of key values can be found in the
- * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/master/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
+ * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/main/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
  * header file. They are prefixed with <tt>GDK_KEY_</tt>.
  */
 namespace Accelerator
diff --git a/gtk/gtkmm/accelkey.h b/gtk/gtkmm/accelkey.h
index e43db678..10a92378 100644
--- a/gtk/gtkmm/accelkey.h
+++ b/gtk/gtkmm/accelkey.h
@@ -35,7 +35,7 @@ namespace Gtk
  *
  * Key values are the codes which are sent whenever a key is pressed or released.
  * The complete list of key values can be found in the
- * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/master/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
+ * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/main/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
  * header file. They are prefixed with <tt>GDK_KEY_</tt>.
  *
  * @ingroup Menus
diff --git a/gtk/src/cellrendereraccel.hg b/gtk/src/cellrendereraccel.hg
index d587bb82..801b4563 100644
--- a/gtk/src/cellrendereraccel.hg
+++ b/gtk/src/cellrendereraccel.hg
@@ -36,7 +36,7 @@ namespace Gtk
  *
  * Key values are the codes which are sent whenever a key is pressed or released.
  * The complete list of key values can be found in the
- * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/master/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
+ * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/main/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
  * header file. They are prefixed with <tt>GDK_KEY_</tt>.
  *
  * @ingroup TreeView
diff --git a/gtk/src/eventcontrollerkey.hg b/gtk/src/eventcontrollerkey.hg
index 38cc720f..888f8fad 100644
--- a/gtk/src/eventcontrollerkey.hg
+++ b/gtk/src/eventcontrollerkey.hg
@@ -31,7 +31,7 @@ class GTKMM_API Widget;
  *
  * Key values are the codes which are sent whenever a key is pressed or released.
  * The complete list of key values can be found in the
- * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/master/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
+ * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/main/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
  * header file. They are prefixed with <tt>GDK_KEY_</tt>.
  *
  * @newin{3,94}
diff --git a/gtk/src/label.hg b/gtk/src/label.hg
index 32641273..ccd5d0da 100644
--- a/gtk/src/label.hg
+++ b/gtk/src/label.hg
@@ -34,7 +34,7 @@ class GTKMM_API Menu;
  *
  * Key values are the codes which are sent whenever a key is pressed or released.
  * The complete list of key values can be found in the
- * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/master/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
+ * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/main/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
  * header file. They are prefixed with <tt>GDK_KEY_</tt>.
  *
  * The Label widget looks like this:
diff --git a/gtk/src/shortcuttrigger.hg b/gtk/src/shortcuttrigger.hg
index 3556cf13..753a12b4 100644
--- a/gtk/src/shortcuttrigger.hg
+++ b/gtk/src/shortcuttrigger.hg
@@ -107,7 +107,7 @@ public:
  *
  * Key values are the codes which are sent whenever a key is pressed or released.
  * The complete list of key values can be found in the
- * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/master/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
+ * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/main/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
  * header file. They are prefixed with <tt>GDK_KEY_</tt>.
  */
 class GTKMM_API KeyvalTrigger : public ShortcutTrigger
@@ -132,7 +132,7 @@ public:
  *
  * Key values are the codes which are sent whenever a key is pressed or released.
  * The complete list of key values can be found in the
- * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/master/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
+ * <a href="https://gitlab.gnome.org/GNOME/gtk/tree/main/gdk/gdkkeysyms.h";>gdk/gdkkeysyms.h</a>
  * header file. They are prefixed with <tt>GDK_KEY_</tt>.
  */
 class GTKMM_API MnemonicTrigger : public ShortcutTrigger