patch 8.2.1020: popupwin test fails in the GUI

Problem:    Popupwin test fails in the GUI.
Solution:   Send GUI byte sequence for <C-S-a>.
diff --git a/src/version.c b/src/version.c
index 5d7e451..b9e6d5b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1020,
+/**/
     1019,
 /**/
     1018,