CI: Run on GitHub Actions

We have Zuul, and we're happy with it; however, every now and then
there's a problem with the managed infrastructure, and there's also
people who contribute patches as GitHub PRs.

Change-Id: I405c5806ed9ad2e7f59f9b2394daf068b373e425

.github/workflows/main.yml

@@ -0,0 +1,27 @@
+on:
+  create:
+  push:
+  pull_request:
+    branches:
+      - master
+
+name: build
+
+jobs:
+  build:
+    name: Tox test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: fedora-python/tox-github-action@v0.4
+        with:
+          tox_env: ${{ matrix.tox_env }}
+          dnf_install: ${{ matrix.dnf_install }}
+    strategy:
+      matrix:
+        tox_env:
+          - py38
+          - py39
+        include:
+          - tox_env: docs
+            dnf_install: graphviz