patch 9.1.1006: PmenuMatch completion highlight can be combined

Problem:  PmenuMatch completion highlight can be combined
Solution: Combine highlight groups PmenuMatch with Pmenu and
          PmenuMatchSel with PmenuSel (glepnir)

fixes: #15563
closes: #16408

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_popup.vim b/src/testdir/test_popup.vim
index 0303c42..08b9cd9 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -1511,6 +1511,16 @@
   call term_sendkeys(buf, "\<ESC>S/non_existing_folder\<C-X>\<C-F>")
   call TermWait(buf, 50)
   call VerifyScreenDump(buf, 'Test_pum_highlights_15', {})
+  call term_sendkeys(buf, "\<C-E>\<Esc>")
+
+  call term_sendkeys(buf, ":hi PmenuMatchSel ctermfg=14\<CR>")
+  call TermWait(buf, 50)
+  call term_sendkeys(buf, ":hi PmenuMatch ctermfg=12\<CR>")
+  call term_sendkeys(buf, ":set cot=menu,noinsert,fuzzy\<CR>")
+  call term_sendkeys(buf, "S\<C-X>\<C-O>")
+  call TermWait(buf, 50)
+  call term_sendkeys(buf, "fb")
+  call VerifyScreenDump(buf, 'Test_pum_highlights_18', {})
 
   call term_sendkeys(buf, "\<C-E>\<Esc>")
   call TermWait(buf)