patch 9.1.0000: Vim 9.1 release

Problem:  Need a new release
Solution: Release Vim 9.1

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/diff.txt b/runtime/doc/diff.txt
index 3caa7cf..91b0047 100644
--- a/runtime/doc/diff.txt
+++ b/runtime/doc/diff.txt
@@ -1,4 +1,4 @@
-*diff.txt*      For Vim version 9.0.  Last change: 2023 Apr 04
+*diff.txt*      For Vim version 9.1.  Last change: 2023 Apr 04
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar