patch 8.2.3961: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/gui_gtk_x11.c b/src/gui_gtk_x11.c
index 2d313f7..ba3993b 100644
--- a/src/gui_gtk_x11.c
+++ b/src/gui_gtk_x11.c
@@ -5071,7 +5071,7 @@
     if (font == NULL)
     {
 	if (report_error)
-	    semsg(_((char *)e_font), name);
+	    semsg(_((char *)e_unknown_font_str), name);
 	return NULL;
     }