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/Make_mvc.mak b/src/Make_mvc.mak
index aaaf530..52282cb 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -1466,7 +1466,7 @@
 	$(MAKE) /NOLOGO -f Make_dos.mak
 	cd ..
 
-testgvim:
+testgvim testgui:
 	cd testdir
 	$(MAKE) /NOLOGO -f Make_dos.mak VIMPROG=..\gvim
 	cd ..