patch 8.2.0311: Vim9: insufficient script tests

Problem:    Vim9: insufficient script tests.
Solution:   Add tests.  Free imports when re-using a script.
diff --git a/src/version.c b/src/version.c
index 61ee30c..ab8cb0e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -739,6 +739,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    311,
+/**/
     310,
 /**/
     309,