CI: Build docker image.

.github/workflows/docker.yml

@@ -0,0 +1,22 @@
+name: Docker image
+
+on:
+  pull_request:
+    branches: [ master ]
+  push:
+    branches: [ master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+
+      - name: Build Docker image
+        uses: docker/build-push-action@v2
+        with:
+          context: .