ci: use ubuntu-latest while arc is unavailable; drop redundant actionlint install

The arc runner pool depends on the in-cluster ARC controller in
kustomize-cluster, which is offline during the libvirt migration.
Move to ubuntu-latest until ARC runners are back.

Drops the manual actionlint download — pre-commit already installs
it via the rhysd/actionlint hook (now pinned to v1.7.12 from the
companion pre-commit-config bump).

Author: xnoto

.github/workflows/_ci.yml

@@ -11,7 +11,9 @@ on:
 jobs:
   lint:
     name: Lint
-    runs-on: arc
+    # ubuntu-latest while arc-dind runners are unavailable during the libvirt
+    # migration. Revert to `arc` once the new k3s cluster has ARC runners up.
+    runs-on: ubuntu-latest
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -21,12 +23,5 @@ jobs:
         with:
           python-version: "3.12"
 
-      - name: Install actionlint
-        run: |
-          mkdir -p "$HOME/.local/bin"
-          curl -sSL https://github.com/rhysd/actionlint/releases/download/v1.7.7/actionlint_1.7.7_linux_amd64.tar.gz | \
-            tar xz -C "$HOME/.local/bin" actionlint
-          echo "$HOME/.local/bin" >> "$GITHUB_PATH"
-
       - name: Run pre-commit
         uses: pre-commit/action@v3.0.1