chore(build): setup Github Action for running tests

TravisCI is moving away from free plans.
The builds have become very slow on travis-ci.org.

This runs the tests on Github Actions as a first step
to assess how well it works.

.github/workflows/test.yml

@@ -0,0 +1,22 @@
+name: test
+on: push
+
+jobs:
+  test:
+    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: Run tests
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          file: ./Dockerfile.test