patch 8.2.3656: Vim9: no error for an evironment variable by itself

Problem:    Vim9: no error for an evironment variable by itself.
Solution:   Give a "without effect" error. (closes #9166)
diff --git a/src/version.c b/src/version.c
index ea77645..e479630 100644
--- a/src/version.c
+++ b/src/version.c
@@ -758,6 +758,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3656,
+/**/
     3655,
 /**/
     3654,