patch 8.2.3906: Vim9 help still contains "under development" warnings

Problem:    Vim9 help still contains "under development" warnings.
Solution:   Remove the explicit warning.
diff --git a/src/version.c b/src/version.c
index 719fe2a..8b9b27e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -750,6 +750,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3906,
+/**/
     3905,
 /**/
     3904,