ci: Lint GitHub Actions workflows with actionlint (#34729)

Added [rhysd/actionlint](https://github.com/rhysd/actionlint/) a static
checker for GitHub Actions workflow files.
Install locally with `brew install actionlint` the run with
`actionlint`.

Inspired by: https://github.com/zed-industries/zed/pull/34704 which
yielded this observation:

> In github actions: 
> 1. strings are truthy
> 2. `${{ }}` will become a string if it doesn't wrap the whole value.
>
> So `if: false && true` becomes `false`
> and `if: ${{ false && true }}` becomes `false`
> but `if: false && ${{ true }}` becomes `"false && true"` which
evaluates true
> The reason you sometimes need `${{ }}` is because YAML doesn't like
`!`
> so `if: !false` is invalid yaml
> and `if: ${{ !false }}` works just fine.

Changes:
- Add `actionlint` job
- Refactor `job_spec` job to be more readable
- Fix all `actionlint` and `shellcheck` errors in Actions workflows (62
in all)
- Add `self-mini-macos` and `self-32vcpu-windows-2022` labels to
self-hosted runners. Not strictly related, but useful if you need to
take a runner out of the rotation (since `macOS`, `self-hosted`, and
`ARM64` are auto-set and cannot be added/removed).
- Change ci.yml macos_relase to target `self-mini-macos` instead of
`bundle` which was previously deprecated.

This would've caught the error fixed in
https://github.com/zed-industries/zed/pull/34704. Here's what that [job
failure](https://github.com/zed-industries/zed/actions/runs/16376993944/job/46279281842?pr=34729)
would've looked like.

Release Notes:

- N/A

.github/workflows/release_nightly.yml

@@ -85,8 +85,7 @@ jobs:
     name: Create a macOS bundle
     if: github.repository_owner == 'zed-industries'
     runs-on:
-      - self-hosted
-      - bundle
+      - self-mini-macos
     needs: tests
     env:
       MACOS_CERTIFICATE: ${{ secrets.MACOS_CERTIFICATE }}
@@ -132,7 +131,7 @@ jobs:
           clean: false
 
       - name: Add Rust to the PATH
-        run: echo "$HOME/.cargo/bin" >> $GITHUB_PATH
+        run: echo "$HOME/.cargo/bin" >> "$GITHUB_PATH"
 
       - name: Install Linux dependencies
         run: ./script/linux && ./script/install-mold 2.34.0