Silence the detachedHead warning when ref_type is a revision

[boblail]

The PR that added this #8622 didn't actually resolve the problem because you see the warning when the @ref_type you've specified is a :revision and you haven't specified a :branch or :tag.

The output looks like this:

==> Checking out revision 3b3527f5050270cf1acd280691b09b5abe130e73
Note: switching to '3b3527f5050270cf1acd280691b09b5abe130e73'

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

   git switch -c <new-branch-name>

Or undo this operation with:

   git switch -

Turn off this advice by setting config variable advice.detachedHead to false

---

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[Bo98]

The PR that added this #8622 didn't actually resolve the problem because you see the warning when the @ref_type you've specified is a :revision and you haven't specified a :branch or :tag.

Makes sense, but what scenario does that extra part in config_repo cover?

[boblail]

The extra part in config_repo covers the scenario where you're upgrading a formula (that uses :revision) that you'd previously installed. If you already have a repo cloned to brew --cache -s <that-formula>, then when you checkout a new revision, git would show that detached head message again unless we reclone it or just set that config in config_repo

[Bo98]

As in a repo cached before the change? Since -c advice.detachedHead=false will automatically set git config for new clones.

[MikeMcQuaid]

I'm fine with this when @Bo98 is.

[boblail]

As in a repo cached before the change?

Yep! Exactly

[Bo98]

Thanks!