Our autobump workflow sets the author and committer to the user who
triggered the workflow, defaulting to @BrewTestBot for scheduled runs.
This can be confusing for maintainers when GitHub shows up as
"Unverified" because the commit is signed with @BrewTestBot's key.[^1]
Let's fix that by configuring our autobump workflow to always commit as
@BrewTestBot, so that the committer matches the GPG signature. To do
that, we need to add support for setting `GIT_COMMITTER_NAME` and
`GIT_COMMITTER_EMAIL`.
[^1]: See, for example, Homebrew/homebrew-core#197234.
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