GitHub workflow CI (lau#133)

.github/workflows/ci.yml

@@ -0,0 +1,70 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+      - ci-test-ghwf
+
+jobs:
+  test:
+    runs-on: ubuntu-22.04
+    env:
+      MIX_ENV: test
+
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - pair:
+              elixir: 1.14.2
+              otp: 25.0
+            lint: lint
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - uses: erlef/setup-beam@v1
+        with:
+          otp-version: ${{ matrix.pair.otp }}
+          elixir-version: ${{ matrix.pair.elixir }}
+
+      - name: Install dependencies
+        run: mix do deps.get --only $MIX_ENV, deps.compile
+
+      - name: Check that there are no unused dependencies in mix.lock
+        run: mix deps.get && mix deps.unlock --check-unused
+        if: ${{ matrix.lint }}
+
+      - name: Compile with --warnings-as-errors
+        run: mix compile --warnings-as-errors
+        if: ${{ matrix.lint }}
+
+      - name: Run tests
+        run: mix test
+
+  test_older_elixir:
+    runs-on: ubuntu-20.04
+    env:
+      MIX_ENV: test
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - pair:
+              elixir: 1.8.1
+              otp: 20.0
+    steps:
+      - uses: actions/checkout@v2
+
+      - uses: erlef/setup-beam@v1
+        with:
+          otp-version: ${{ matrix.pair.otp }}
+          elixir-version: ${{ matrix.pair.elixir }}
+
+      - name: Install dependencies
+        run: mix do deps.get --only $MIX_ENV, deps.compile
+
+      - name: Run tests
+        run: mix test