github: Add an actionlint github workflow

Add a new github actions workflow that will perform linting on github
actions workflow changes. It will only run if github workflows are
modified.

Signed-off-by: Russell Bryant <rbryant@redhat.com>

.github/workflows/actionlint.dockerfile

@@ -0,0 +1,3 @@
+# Since dependabot cannot update workflows using docker,
+# we use this indirection since dependabot can update this file.
+FROM docker.io/rhysd/actionlint:1.7.1@sha256:435ecdb63b1169e80ca3e136290072548c07fc4d76a044cf5541021712f8f344

.github/workflows/actionlint.yml

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+name: Lint GitHub Actions workflows
+on:
+  push:
+    branches:
+      - "main"
+    paths:
+      - '.github/workflows/*.ya?ml'
+      - '.github/workflows/actionlint.*'
+  pull_request:
+    branches:
+      - "main"
+    paths:
+      - '.github/workflows/*.ya?ml'
+      - '.github/workflows/actionlint.*'
+
+env:
+  LC_ALL: en_US.UTF-8
+
+defaults:
+  run:
+    shell: bash
+
+permissions:
+  contents: read
+
+jobs:
+  actionlint:
+    runs-on: ubuntu-latest
+    steps:
+      - name: "Checkout"
+        uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4.1.7
+        with:
+          fetch-depth: 0
+
+      - name: "Download actionlint"
+        run: |
+          docker build --tag actionlint - < .github/workflows/actionlint.dockerfile
+
+      - name: "Check workflow files"
+        run: |
+          echo "::add-matcher::.github/workflows/matchers/actionlint.json"
+          docker run --volume="${PWD}:/repo" --workdir=/repo actionlint -color

.github/workflows/matchers/actionlint.json

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+{
+  "problemMatcher": [
+    {
+      "owner": "actionlint",
+      "pattern": [
+        {
+          "regexp": "^(?:\\x1b\\[\\d+m)?(.+?)(?:\\x1b\\[\\d+m)*:(?:\\x1b\\[\\d+m)*(\\d+)(?:\\x1b\\[\\d+m)*:(?:\\x1b\\[\\d+m)*(\\d+)(?:\\x1b\\[\\d+m)*: (?:\\x1b\\[\\d+m)*(.+?)(?:\\x1b\\[\\d+m)* \\[(.+?)\\]$",
+          "file": 1,
+          "line": 2,
+          "column": 3,
+          "message": 4,
+          "code": 5
+        }
+      ]
+    }
+  ]
+}