Use GitHub Actions for CI

.github/workflows/elixir.yml

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+name: Elixir CI
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+permissions:
+  contents: read
+
+env:
+  ImageOs: ubuntu20
+
+jobs:
+  build:
+
+    name: Build and test
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+    - name: Set up Elixir
+      uses: erlef/setup-beam@988e02bfe678367a02564f65ca2e37726dc0268f
+      with:
+        elixir-version: '1.14.1' # Define the elixir version [required]
+        otp-version: '24' # Define the OTP version [required]
+    - name: Restore dependencies cache
+      uses: actions/cache@v3
+      with:
+        path: deps
+        key: ${{ runner.os }}-mix-${{ hashFiles('**/mix.lock') }}
+        restore-keys: ${{ runner.os }}-mix-
+    - name: Install dependencies
+      run: mix deps.get
+    - name: Run tests
+      run: mix test