patch 8.1.0921: terminal test sometimes fails; using memory after free

Problem:    Terminal test sometimes fails; using memory after free.
Solution:   Fee memory a bit later.  Add test to cover this.  Disable flaky
            screenshot test. (closes #3956)
diff --git a/src/version.c b/src/version.c
index e3ec215..d0857e7 100644
--- a/src/version.c
+++ b/src/version.c
@@ -784,6 +784,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    921,
+/**/
     920,
 /**/
     919,