docker.yml: Set persist-credentials: false

[sjackman]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
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• Have you successfully run brew tests with your changes locally?

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Aesthetic change only.

[MikeMcQuaid]

Why are actions/checkout and git fetch origin master both needed?

[jonchang]

I don't believe it fetches branch refs, even with fetch-depth: 0

[MikeMcQuaid]

In that case I'd suggest doing something like this: https://github.com/actions/checkout#Fetch-all-branches

[sjackman]

Why? We don't need all branches, just origin/master. I prefer the simplest command that does the job. I'm addressing this specific error:

$ docker run -it --rm docker.pkg.github.com/homebrew/brew/ubuntu20.04:2.2.15
$ brew update
fatal: ambiguous argument 'refs/remotes/origin/master': unknown revision or path not in the working tree.

[MikeMcQuaid]

+refs/heads/#{ENV["GITHUB_BASE_REF"]} is the refspec you want. It would be nice to combine that with the normal fetch for actions/checkout to avoid running two git fetches.

[sjackman]

git fetch origin master takes 1.36s, so it doesn't seem worth optimizing to me.

actions/checkout does not currently support fetching multiple references. There's an open issue. actions/checkout#214