ci: Check formatting and code style on GitHub Actions

.github/workflows/lint.yml

@@ -0,0 +1,34 @@
+# Create initial workflow based on GitHub's suggestion for Elixir.
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["main"]
+
+jobs:
+  lint:
+    name: Lint codebase
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up Elixir
+        uses: erlef/setup-beam
+        with:
+          elixir-version: '1.16.0'
+          otp-version: '26.0'
+      - name: Cache dependencies
+        uses: actions/cach@v3
+        with:
+          path: deps
+          key: ${{ runner.os }}-mix-${{ hashFiles('**/mix.lock') }}
+          restore-keys: ${{ runner.os }}-mix-
+      - name: Install dependencies
+        run: mix deps.get
+
+      - name: Check formatting
+        run: mix format --check-formatted
+
+      - name: Check code style
+        run: mix credo
+