patch 8.2.4964: MS-Windows GUI: mouse event test is flaky

Problem:    MS-Windows GUI: mouse event test is flaky.
Solution:   Add a short delay after generating a mouse event.
diff --git a/src/version.c b/src/version.c
index fddf7d9..1b98b03 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4964,
+/**/
     4963,
 /**/
     4962,