[gnote] Put internal constants to anonymous namespace

[Aurimas Černius <aurimasc src gnome org>]

commit cb9723e8ed91edacafeed06cbcf547b4ac0b97a4
Author: Aurimas Černius <aurisc4 gmail com>
Date:   Sun Dec 13 13:10:51 2020 +0200

    Put internal constants to anonymous namespace

 src/preferences.cpp | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/preferences.cpp b/src/preferences.cpp
index 3eae761d..a9a0e621 100644
--- a/src/preferences.cpp
+++ b/src/preferences.cpp
@@ -22,6 +22,7 @@
 
 #include "preferences.hpp"
 
+namespace {
 
 const char *SCHEMA_DESKTOP_GNOME_INTERFACE = "org.gnome.desktop.interface";
 const char *SCHEMA_SYNC = "org.gnome.gnote.sync";
@@ -30,6 +31,8 @@ const Glib::ustring SYNC_CLIENT_ID = "sync-guid";
 const Glib::ustring SYNC_LOCAL_PATH = "sync-local-path";
 const Glib::ustring SYNC_CONFIGURED_CONFLICT_BEHAVIOR = "sync-conflict-behavior";
 
+}
+
 namespace gnote {