Lock the master branch during release builds

[daniel-beck]

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Feature Request

GitHub rulesets allow defining flexible (and stacking) rules for branches: https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/managing-rulesets/about-rulesets

We occasionally need to deal with PR merges happening during a (weekly) release build, so it seems it would be useful to lock the master branch for changes while the build is ongoing. This could even carve out an exception for the account pushing the release commits (needs to be a team, but easy enough to define), so it could "wrap" the release build rather than needing to "interleave" it.