ci: add GitHub actions

Author: Ovyerus

.github/workflows/push.yaml

@@ -0,0 +1,21 @@
+name: Push
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  docker:
+    name: Lint and test
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Nix
+        uses: nixbuild/nix-quick-install-action@v30
+
+      - run: nix flake check
+      - run: nix develop --command mix deps.get
+      - run: nix develop --command mix credo
+      - run: nix develop --command mix test