Add github action updater

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

.github/workflows/gh-actions-updater.yaml

@@ -0,0 +1,23 @@
+name: GitHub Actions Version Updater
+
+# Controls when the action will run.
+on:
+  schedule:
+    # Automatically run on every Sunday
+    - cron: "0 0 * * 0"
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          # [Required] Access token with `workflow` scope.
+          token: ${{ secrets.WORKFLOW_SECRET }}
+
+      - name: Run GitHub Actions Version Updater
+        uses: saadmk11/github-actions-version-updater@v0.7.1
+        with:
+          # [Required] Access token with `workflow` scope.
+          token: ${{ secrets.WORKFLOW_SECRET }}