[gtksourceview] build: fix annoying GCC 12 dangling-pointer

[Christian Hergert <chergert src gnome org>]

commit ab26083a3b58aa84966eb1df917205d646a7bf2a
Author: Christian Hergert <chergert redhat com>
Date:   Fri Feb 11 15:28:17 2022 -0800

    build: fix annoying GCC 12 dangling-pointer

 meson.build | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/meson.build b/meson.build
index 60598980..0b9c9380 100644
--- a/meson.build
+++ b/meson.build
@@ -250,6 +250,7 @@ else
     '-Wmissing-noreturn',
     '-Wnested-externs',
     '-Wno-cast-function-type',
+    '-Wno-dangling-pointer',
     '-Wno-missing-field-initializers',
     '-Wno-sign-compare',
     '-Wno-unused-parameter',