patch 8.2.0503: Vim9: some code is not tested

Problem:    Vim9: some code is not tested.
Solution:   Add tests.  Fix uncovered problems.
diff --git a/src/version.c b/src/version.c
index ddc5295..528454b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -739,6 +739,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    503,
+/**/
     502,
 /**/
     501,