runtime: Set b:undo_ftplugin where missing (#12943)

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
index d8130ce..4fafc7c 100644
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -158,6 +158,7 @@
 runtime/ftplugin/i3config.vim		@hiqua
 runtime/ftplugin/icon.vim		@dkearns
 runtime/ftplugin/indent.vim		@dkearns
+runtime/ftplugin/ishd.vim		@dkearns
 runtime/ftplugin/j.vim			@glts
 runtime/ftplugin/javascript.vim		@dkearns
 runtime/ftplugin/javascriptreact.vim	@dkearns