github/workflows/lint: add mypy linting

Not everything is typed in our scripts, but this is just to make sure
current code passes linting. More typing can be added in the future.

.github/workflows/lint.yml

@@ -40,6 +40,15 @@ jobs:
       - uses: actions/checkout@v4
       - uses: astral-sh/ruff-action@v2
 
+  mypy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: python/mypy@master
+        with:
+          install_project_dependencies: no
+          options: '--check-untyped-defs'
+
   editorconfig:
     runs-on: ubuntu-latest
     steps: