t3700: avoid suppressing git's exit code

t3700: avoid suppressing git's exit code

Replace pipelines involving git commands with temporary files (actual)
to ensure that any crashes or unexpected exit codes from the git
commands are properly caught by the test suite. A simple pipeline
like 'git foo | grep bar' ignores the exit code of 'git', which
can hide regressions.

In cases where we were counting lines with 'wc -l' to ensure a
pattern was absent, simplify the logic to use '! grep' to avoid
subshells entirely.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Siddharth Shrimali <r.siddharth.shrimali@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>