patch 8.2.3911: Vim9: type check for filter() does not accept unknown

Problem:    Vim9: type check for filter() does not accept unknown.
Solution:   Also accept unknown for the return type. (closes #9413)
diff --git a/src/version.c b/src/version.c
index 8c4377b..0d99bb8 100644
--- a/src/version.c
+++ b/src/version.c
@@ -750,6 +750,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3911,
+/**/
     3910,
 /**/
     3909,