release version 9.0

Problem:    About time to release Vim 9.0.
Solution:   Update the version number everywhere.
diff --git a/runtime/doc/usr_toc.txt b/runtime/doc/usr_toc.txt
index 59777cc..655d6a9 100644
--- a/runtime/doc/usr_toc.txt
+++ b/runtime/doc/usr_toc.txt
@@ -1,4 +1,4 @@
-*usr_toc.txt*	For Vim version 8.2.  Last change: 2022 Jun 20
+*usr_toc.txt*	For Vim version 9.0.  Last change: 2022 Jun 20
 
 		     VIM USER MANUAL - by Bram Moolenaar