Remove try/auto homu branch protections from rust-lang/rust

[Kobzol]

To be merged once we get rid of homu. We should double-check that homu no longer has access to push to these branches (including main) after this is merged. We can also delete the try and auto branches after this is merged.

[github-actions]

Dry-run check results

[WARN  sync_team] sync-team is running in dry mode, no changes will be applied.
[INFO  sync_team] synchronizing crates-io
[INFO  sync_team] synchronizing github
[INFO  sync_team] 💻 Repo Diffs:
    📝 Editing repo 'rust-lang/bors':
      Rulesets:
          Ruleset for main
            No changes
    📝 Editing repo 'rust-lang/rust':
      Environments:
        🔄 Update: bors
            Removing branches: auto, try

[Kobzol]

I don't think that there is any point in returning to homu now, so we can merge this.

[Mark-Simulacrum]

I think we want to delete the branches before/after merging this, right? Then they will no longer be used at all because we have the "cannot create branch" protection as well.

I think before doing that we should try to double check that there's no AWS and/or GitHub state that references the branch name in OIDC or environment rules or similar, to avoid accidentally exposing credentials to some future creator of the branch name. I'm not sure if there's an authoritative way to do that unfortunately, but at minimum they should be removed from the bors environment (https://github.com/rust-lang/rust/settings/environments/5453059056/edit).

[Kobzol]

This PR actually removes them from the bors environment, we can do that through team now :) Not sure about the OIDC stuff though, will check simpleinfra.

[Kobzol]

Haven't found any references in simpleinfra, I think/hope we migrated everything to the bors environment when we switched off rust-lang-ci last year.