patch 8.2.3899: Vim9: test for map() on string fails

Problem:    Vim9: test for map() on string fails.
Solution:   Expect string return type.
diff --git a/src/version.c b/src/version.c
index e41dcb1..260182b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -750,6 +750,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3899,
+/**/
     3898,
 /**/
     3897,