patch 8.2.3709: Vim9: backtick expression expanded when not desired

Problem:    Vim9: backtick expression expanded when not desired.
Solution:   Only expand a backtick expression for commands that expand their
            argument.  Remove a few outdated TODO comments.
diff --git a/src/version.c b/src/version.c
index b26746b..be24950 100644
--- a/src/version.c
+++ b/src/version.c
@@ -754,6 +754,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3709,
+/**/
     3708,
 /**/
     3707,