patch 8.2.2030: some tests fail on Mac

Problem:    Some tests fail on Mac.
Solution:   Avoid Mac test failures.  Add additional test for wildmenu.
            (Yegappan Lakshmanan, closes #7341)
diff --git a/src/testdir/test_popupwin.vim b/src/testdir/test_popupwin.vim
index e5d4697..45e3503 100644
--- a/src/testdir/test_popupwin.vim
+++ b/src/testdir/test_popupwin.vim
@@ -605,6 +605,7 @@
 	endfor
 	%foldclose
 	set shell=/bin/sh noruler
+	unlet $PROMPT_COMMAND
 	let $PS1 = 'vim> '
         terminal ++rows=4
 	$wincmd w