[PATCH] tests: shell negation portability fix

Commit 969c8775 introduced a test which uses the non-portable construct:

  command1 && ! command2 | command3

which must be

  command1 && ! (command2 | command3)

to work on bsd shells (this is another example of bbf08124, which fixed
several similar cases).

Signed-off-by: Jeff King <redacted>
---
I had totally forgotten about this monstrosity until my autobuild broke.

diff --git a/t/t4128-apply-root.sh b/t/t4128-apply-root.sh
index bc7a8a8..8f6aea4 100755
--- a/t/t4128-apply-root.sh
+++ b/t/t4128-apply-root.sh

@@ -72,7 +72,7 @@ test_expect_success 'apply --directory (delete file)' '
 	echo content >some/sub/dir/delfile &&
 	git add some/sub/dir/delfile &&
 	git apply --directory=some/sub/dir/ --index patch &&
-	! git ls-files | grep delfile
+	! (git ls-files | grep delfile)
 '
 
 cat > patch << 'EOF'