adding back actions

.github/workflows/README.md

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+# GitHub Workflows
+
+Use `act` for testing workflows locally: https://nektosact.com/introduction.html

.github/workflows/ci.yaml

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+name: CI
+
+on:
+  push:
+  pull_request:
+    branches: [main]
+  workflow_dispatch:
+
+concurrency:
+  # Cancel previous actions from the same PR: https://stackoverflow.com/a/72408109
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  format:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Setup Bazel
+        uses: bazel-contrib/[email protected]
+        with:
+          bazelisk-cache: true
+          disk-cache: ${{ github.workflow }}
+          repository-cache: true
+          bazelrc: |
+            build --color=yes
+            build --show_timestamps
+      - name: Format Repository
+        run: bazel run //:format