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  Remove a few outdated TODO comments.

src/version.c

@@ -753,6 +753,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3709,
 /**/
     3708,
 /**/