t2203: avoid suppressing git status exit code

t2203: avoid suppressing git status exit code

When git status is piped into grep, the exit status of the Git
command is hidden by the pipeline. Capture the status output in a
temporary file first, and then filter it as needed, so that any
failure from git status is still noticed by the test suite.

Signed-off-by: Jialong Wang <jerrywang183@yahoo.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>