patch 8.2.0715: Vim9: leaking memory

Problem:    Vim9: leaking memory.
Solution:   Free strings after concatenating them.
diff --git a/src/version.c b/src/version.c
index fd59afd..7434486 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    715,
+/**/
     714,
 /**/
     713,