ci: allow commits on top of beta PRs

[gigamonster256]

any commits (CI or otherwise) on top of the authoritative beta PRs (ones with beta tag) would make tree hash mis-match and trigger a force push

the first commit relaxes this to allow the beta branch to remain as long as the beta branch history contains all beta PRs and is based on current dev branch

before:
only dev..beta_PRs

after:
allows dev..beta_PRs..extra_commits

the second commit takes advantage of this relaxation to apply nix-hash updates to the beta branch as needed

feel free to close if this is not the correct model for the beta branch

related: #11919

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found

[github-actions]

Hey! Your PR title ci: allow commits on top of beta PRs doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.