patch 9.1.0677: :keepp does not retain the substitute pattern

Problem:  :keeppatterns does not retain the substitute pattern
          for a :s command
Solution: preserve the last substitute pattern when used with the
          :keeppatterns command modifier (Gregory Anders)

closes: #15497

Signed-off-by: Gregory Anders <greg@gpanders.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/version9.txt b/runtime/doc/version9.txt
index 73e54a1..3729590 100644
--- a/runtime/doc/version9.txt
+++ b/runtime/doc/version9.txt
@@ -1,4 +1,4 @@
-*version9.txt*  For Vim version 9.1.  Last change: 2024 Jul 30
+*version9.txt*  For Vim version 9.1.  Last change: 2024 Aug 15
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -41592,6 +41592,7 @@
   mark deprecated attributes from LSP server) |complete-items|
 - the regex engines match correctly case-insensitive multi-byte characters
   (and apply proper case folding)
+- |:keeppatterns| preserves the last substitute pattern when used with |:s|
 
 							*added-9.2*
 Added ~