patch 9.1.0915: GVim: default font size a bit too small

Problem:  GVim: default font size a bit too small
Solution: increase guifont size to 12 pt on GTK builds
          of gVim (matveyt).

fixes: #16172
closes: #16178

Signed-off-by: matveyt <matthewtarasov@yandex.ru>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/gui_gtk_x11.c b/src/gui_gtk_x11.c
index 6c97d1a..c037702 100644
--- a/src/gui_gtk_x11.c
+++ b/src/gui_gtk_x11.c
@@ -160,7 +160,7 @@
  * "Monospace" is a standard font alias that should be present
  * on all proper Pango/fontconfig installations.
  */
-# define DEFAULT_FONT	"Monospace 10"
+# define DEFAULT_FONT	"Monospace 12"
 
 #if defined(FEAT_GUI_GNOME) && defined(FEAT_SESSION)
 # define USE_GNOME_SESSION