Auto merge of #144244 - jieyouxu:pr-full-ci, r=Kobzol

Enforce that PR CI jobs are a subset of Auto CI jobs modulo carve-outs

### Background

Currently, it is possible for a PR with red PR-only CI to pass Auto CI, then all subsequent PR CI runs will be red until that is fixed, even in completely unrelated PRs. For instance, this happened with PR-CI-only Spellcheck (rust-lang/rust#144183).

See more discussions at [#t-infra > Spellcheck workflow now fails on all PRs (tree bad?)](https://rust-lang.zulipchat.com/#narrow/channel/242791-t-infra/topic/Spellcheck.20workflow.20now.20fails.20on.20all.20PRs.20.28tree.20bad.3F.29/with/529769404).

### CI invariant: PR CI jobs are a subset of Auto CI jobs modulo carve-outs

To prevent red PR CI in completely unrelated subsequent PRs and PR CI runs, we need to maintain an invariant that **PR CI jobs are a subset of Auto CI jobs modulo carve-outs**.

This is **not** a "strict" subset relationship: some jobs necessarily have to differ under PR CI and Auto CI environments, at least in the current setup. Still, we can try to enforce a weaker "subset modulo carve-outs" relationship between CI jobs and their corresponding Auto jobs. For instance:

- `x86_64-gnu-tools` will have `auto`-only env vars like `DEPLOY_TOOLSTATES_JSON: toolstates-linux.json`.
- `tidy` will want to `continue_on_error: true` in PR CI to allow for more "useful" compilation errors to also be reported, whereas it should be `continue_on_error: false` in Auto CI to prevent wasting Auto CI resources.

The **carve-outs** are:

1. `env` variables.
2. `continue_on_error`.

We enforce this invariant through `citool`, so only affects job definitions that are handled by `citool`. Notably, this is not sufficient *alone* to address the CI-only Spellcheck issue (rust-lang/rust#144183). To carry out this enforcement, we modify `citool` to auto-register PR jobs as Auto jobs with `continue_on_error` overridden to `false` **unless** there's an overriding Auto job for the PR job of the same name that only differs by the permitted **carve-outs**.

### Addressing the Spellcheck PR-only CI issue

Note that Spellcheck currently does not go through `citool` or `bootstrap`, and is its own GitHub Actions workflow. To actually address the PR-CI-only Spellcheck issue (rust-lang/rust#144183), and carry out the subset-modulo-carve-outs enforcement universally, this PR additionally **removes the current Spellcheck implementation** (a separate GitHub Actions Workflow). That is incompatible with Homu unless we do some hacks in the main CI workflow.

This effectively partially reverts rust-lang/rust#134006 (the separate workflow part, not the tidy extra checks component), but is not prejudice against relanding the `typos`-based spellcheck in another implementation that goes through the usual bootstrap CI workflow so that it does work with Homu. The `typos`-based spellcheck seems to have a good false-positive rate.

Closes rust-lang/rust#144183.

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r? infra-ci

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