Add linters workflow

.github/workflows/linters.yml

@@ -0,0 +1,18 @@
+name: Linters
+
+on: [push, workflow_dispatch]
+
+jobs:
+
+  mypy:
+    name: Run mypy
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+        with:
+          python-version: 3.9
+      - run: pip install tox
+      - run: tox
+        env:
+          TOXENV: mypy