quell an annoying warning; this use is likely safe

cvs2git

@@ -1,7 +1,7 @@
 #!/bin/mksh
 # -*- mode: sh -*-
 #-
-# Copyright © 2014, 2015, 2017
+# Copyright © 2014, 2015, 2017, 2020
 #	mirabilos <[email protected]>
 #
 # Provided that these terms and disclaimer and all copyright notices
@@ -211,6 +211,7 @@ if (( do_grafts )); then
 	done
 	# make graft permanent
 	if [[ -s info/grafts ]]; then
+		FILTER_BRANCH_SQUELCH_WARNING=1 \
 		$git filter-branch --tag-name-filter cat -- --all || \
 		    die "git filter-branch failed with errorlevel $?"
 		rm -f info/grafts