t4001: don't run 'git status' upstream of a pipe

t4001: don't run 'git status' upstream of a pipe

The primary purpose of three tests in 't4001-diff-rename.sh' is to
check rename detection in 'git status', but all three do so by running
'git status' upstream of a pipe, hiding its exit code.  Consequently,
the test could continue even if 'git status' exited with error.

Use an intermediate file between 'git status' and 'test_i18ngrep' to
catch a potential failure of the former.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>