fix: add github ci

.github/workflows/ci.yml

@@ -0,0 +1,18 @@
+on: push
+
+jobs:
+  test:
+    runs-on: ubuntu-20.04
+    name: OTP ${{matrix.otp}} / Elixir ${{matrix.elixir}}
+    strategy:
+      matrix:
+        otp: ['24.2']
+        elixir: ['1.13.2', '1.14.3']
+    steps:
+      - uses: actions/checkout@v4
+      - uses: erlef/setup-beam@v1
+        with:
+          otp-version: ${{matrix.otp}}
+          elixir-version: ${{matrix.elixir}}
+      - run: mix deps.get
+      - run: mix test