patch 8.2.3180: Vim9: memory leak when concatenating to an imported string

Problem:    Vim9: memory leak when concatenating to an imported string.
Solution:   Clear the destination.
diff --git a/src/version.c b/src/version.c
index 48e6748..b59eca2 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3180,
+/**/
     3179,
 /**/
     3178,