patch 8.2.5084: when the GUI shows a dialog tests get stuck

Problem:    When the GUI shows a dialog tests get stuck.
Solution:   Add the --gui-dialog-file argument.
diff --git a/src/proto/gui.pro b/src/proto/gui.pro
index 209e7f1..2a0ac80 100644
--- a/src/proto/gui.pro
+++ b/src/proto/gui.pro
@@ -67,4 +67,5 @@
 int gui_do_findrepl(int flags, char_u *find_text, char_u *repl_text, int down);
 void gui_handle_drop(int x, int y, int_u modifiers, char_u **fnames, int count);
 int check_for_interrupt(int key, int modifiers_arg);
+int gui_dialog_log(char_u *title, char_u *message);
 /* vim: set ft=c : */