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/nix.yml

@@ -43,8 +43,8 @@ jobs:
       - name: Set path
         if: ${{ ! matrix.system.install_nix }}
         run: |
-          echo "/nix/var/nix/profiles/default/bin" >> $GITHUB_PATH
-          echo "/Users/administrator/.nix-profile/bin" >> $GITHUB_PATH
+          echo "/nix/var/nix/profiles/default/bin" >> "$GITHUB_PATH"
+          echo "/Users/administrator/.nix-profile/bin" >> "$GITHUB_PATH"
 
       - uses: cachix/install-nix-action@02a151ada4993995686f9ed4f1be7cfbb229e56f # v31
         if: ${{ matrix.system.install_nix }}
@@ -56,11 +56,13 @@ jobs:
           name: zed
           authToken: "${{ secrets.CACHIX_AUTH_TOKEN }}"
           pushFilter: "${{ inputs.cachix-filter }}"
-          cachixArgs: '-v'
+          cachixArgs: "-v"
 
       - run: nix build .#${{ inputs.flake-output }} -L --accept-flake-config
 
       - name: Limit /nix/store to 50GB on macs
         if: ${{ ! matrix.system.install_nix }}
         run: |
-          [ $(du -sm /nix/store | cut -f1) -gt 50000 ] && nix-collect-garbage -d || :
+          if [ "$(du -sm /nix/store | cut -f1)" -gt 50000 ]; then
+            nix-collect-garbage -d || true
+          fi