Add mypy check

.github/workflows/check.yml

@@ -1,4 +1,4 @@
-name: style + docs check
+name: style|docs|types
 
 on:
   pull_request:
@@ -12,9 +12,9 @@ jobs:
         working-directory: .
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Set up Python 3.10
-        uses: actions/setup-python@v4
+        uses: actions/setup-python@v5
         with:
           python-version: "3.10"
           cache: 'pip'
@@ -26,3 +26,8 @@ jobs:
         run: black src --check --diff
       - name: Check that documentation can be built
         run: tox -e docs
+      - name: Check python types with mypy
+        run: |
+          pip install mypy
+          mypy --install-types
+          mypy src/