notes-utils: free note trees when releasing copied notes

While we clear most of the members of `struct notes_rewrite_cfg` in
`finish_copy_notes_for_rewrite()`, we do not clear the notes tree. Fix
this to plug this memory leak.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

notes-utils.c

@@ -187,6 +187,7 @@ void finish_copy_notes_for_rewrite(struct repository *r,
 	for (i = 0; c->trees[i]; i++) {
 		commit_notes(r, c->trees[i], msg);
 		free_notes(c->trees[i]);
+		free(c->trees[i]);
 	}
 	free(c->trees);
 	free(c);