patch 8.2.2257: Vim9: using -> for lambda is ambiguous

Problem:    Vim9: using -> for lambda is ambiguous.
Solution:   Stop supporting ->, must use =>.
diff --git a/src/version.c b/src/version.c
index 75813ed..f5d57e2 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2257,
+/**/
     2256,
 /**/
     2255,