CI: Add initial GitHub Actions configuration

Fixes: rpm-software-management#2569

.github/workflows/linux.yml

@@ -0,0 +1,16 @@
+name: Linux CI
+
+on: [push, pull_request]
+
+jobs:
+  build_and_test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Build the Fedora testing environment
+        run: sudo ./mktree.docker build
+        working-directory: ./tests
+      - name: Run the test suite
+        run: sudo ./mktree.docker check --interactive=false -j$(nproc)
+        working-directory: ./tests