t/{t5541,lib-httpd}: replace problematic '!()' notation with test_must_fail

The '!()' notation is interpreted as a pattern-list on Ksh.  The Ksh man
page describe it as follows:

   !(pattern-list)
      Matches anything except one of the given patterns.

Ksh performs a file glob using the pattern-list and then tries to execute
the first file in the list.  If a space is added between the '!' and the
open parens, then Ksh will not interpret it as a pattern list, but in this
case, it is preferred to use test_must_fail, so lets do so.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-httpd.sh

@@ -145,7 +145,7 @@ test_http_push_nonff() {
 		echo "changed" > path2 &&
 		git commit -a -m path2 --amend &&
 
-		!(git push -v origin >output 2>&1) &&
+		test_must_fail git push -v origin >output 2>&1 &&
 		(cd "$REMOTE_REPO" &&
 		 test $HEAD = $(git rev-parse --verify HEAD))
 	'