fix brown paper bag breakage in t5150-request-pull.sh

The recent addition to the test case 'pull request format' interrupted
the single-quoted text, effectively adding a third argument to the
test_expect_success command. Since we do not have a prerequisite named
"pull request format", the test is skipped, no matter what. Additionally,
the file name argument to the grep command is missing. Fix both issues.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>