t/helper: initialize repository if necessary
The repository helper is used in t5318 to read commit graphs whether
we're in a repository or not. However, without a repository, we have no
way to properly initialize the hash algorithm, meaning that the file is
misread.
Fix this by calling setup_git_directory_gently, which will read the
environment variable the testsuite sets to ensure that the correct hash
algorithm is set.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>