release version 9.0

Problem:    About time to release Vim 9.0.
Solution:   Update the version number everywhere.
diff --git a/runtime/doc/insert.txt b/runtime/doc/insert.txt
index 8c35798..b376af7 100644
--- a/runtime/doc/insert.txt
+++ b/runtime/doc/insert.txt
@@ -1,4 +1,4 @@
-*insert.txt*    For Vim version 8.2.  Last change: 2022 Apr 06
+*insert.txt*    For Vim version 9.0.  Last change: 2022 Apr 06
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar