patch 8.2.4276: separate test function for the GUI scrollbar

Problem:    Separate test function for the GUI scrollbar.
Solution:   Use test_gui_event(). (Yegappan Lakshmanan, closes #9674)
diff --git a/src/version.c b/src/version.c
index d3b7bf8..301f544 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4276,
+/**/
     4275,
 /**/
     4274,