.github/workflows: Add docker build check (#8345)

Fixes #8344

Signed-off-by: Claire Wang <claire@tailscale.com>

.github/workflows/docker-file-build.yml

@@ -0,0 +1,15 @@
+name: "Dockerfile build"
+on: 
+  push:
+    branches:
+    - main
+  pull_request:
+    branches:
+      - "*"
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: "Build Docker image"
+      run: docker build .