patch 8.2.0420: Vim9: cannot interrupt a loop with CTRL-C

Problem:    Vim9: cannot interrupt a loop with CTRL-C.
Solution:   Check for CTRL-C once in a while.  Doesn't fully work yet.
diff --git a/src/version.c b/src/version.c
index 26939bb..1ad99cf 100644
--- a/src/version.c
+++ b/src/version.c
@@ -739,6 +739,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    420,
+/**/
     419,
 /**/
     418,