Deduplicate CI on PRs

[StanFromIreland]

Fixes:

That is, the CI is run twice.

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📚 Documentation preview 📚: https://docs-community--171.org.readthedocs.build/

[hugovk]

Please don't disable pushes for feature branches, I want to test on my fork before opening a PR.

[bskinn]

Please don't disable pushes for feature branches, I want to test on my fork before opening a PR.

Could add an opt-in flag instead of disabling entirely.
[run ci], say... the opposite of [skip ci].

[hugovk]

I don't think it's worth it:

• First, we shouldn't create PRs from branches in this repo -- do it from your fork.
• The CI is disabled by default for forks, so it'll only run in your fork when you have explicitly enabled it.
• If you've enabled it for your fork, you have full control to disable it.
• Technically speaking, these are not duplicate runs. The push trigger runs whatever is on the branch. The PR trigger simulates a merge and runs that, which sometimes has different results and fails in one but not the other.
• The CI only takes 12 seconds to run.

Root cause: #170 was made from a branch in this repo and had the "duplicate" CI.

Should triagers have write permission to create branches here?

Should the core team?

We've disabled it for some repos (cpython, peps).

[StanFromIreland]

Root cause: #170 was made from a branch in this repo and had the "duplicate" CI.

Oh, I did not realise, I used the builtin editor.