Fix a bug where test-autopatch would fail in an env where no global git config is set
Fix a bug where test-autopatch would fail in an env where no global git config is set

Summary: See title.

Test Plan:
In environments with and without global git config set:
`ninja check-source-control-tools`

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D4635

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