CI: use GH Actions

.github/workflows/tests.yaml

@@ -0,0 +1,23 @@
+name: Tests
+on: [push, pull_request]
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python:
+          - '2.7'
+          - '3.5'
+          - '3.6'
+          - '3.7'
+          - '3.8'
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python }}
+          cache: 'pip'
+          cache-dependency-path: 'setup.oy'
+      - run: pip install -e .[test]
+      - run: py.test --cov=promise tests