Add action to build docker image

Signed-off-by: Olivier Vernin <olivier@vernin.me>

Author: olblak

.github/workflows/docker.yaml

@@ -0,0 +1,24 @@
+---
+name: docker
+# Testing that we can still build the docker image used by Github Action
+
+on:
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      - name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          push: false
+          tags: updatecli/updatecli-action