[PATCH] Add a test for git-config --file

Check for non-0 exit code if the confiog file does not exist and
if it works exactly like when setting GIT_CONFIG.

Signed-off-by: Alex Riesen <redacted>
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 t/t1300-repo-config.sh |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)