release version 9.0

Problem:    About time to release Vim 9.0.
Solution:   Update the version number everywhere.
diff --git a/src/Makefile b/src/Makefile
index b33b2a2..95fe0d4 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1039,8 +1039,8 @@
 MAN1DIR = /man1
 
 ### Vim version (adjusted by a script)
-VIMMAJOR = 8
-VIMMINOR = 2
+VIMMAJOR = 9
+VIMMINOR = 0
 
 ### Location of Vim files (should not need to be changed, and  {{{1
 ### some things might not work when they are changed!)