Add MyPy action for CI

.github/workflows/tests.yml

@@ -47,6 +47,24 @@ jobs:
         run: ${{ matrix.command }}
 
 
+  mypy:
+    runs-on: ubuntu-18.04
+
+    container:
+      image: python:3.7
+
+    name: MyPy
+
+    steps:
+      - name: Check out repository code
+        uses: actions/checkout@v2
+      - name: Install dependencies
+        run: pip install -r requirements-dev.txt
+      - name: Add localsettings
+        run: cp evap/settings_test.py evap/localsettings.py
+      - name: Run MyPy
+        run: mypy -p evap
+
   linter:
     runs-on: ubuntu-18.04