Make MyPy happy

Fixes for various type errors throw by mypy.

portal/api/rest.py

@@ -5,7 +5,7 @@ from .blueprint import bp
 
 
 @bp.get("/<path:_>")
-def fallback_not_found(_: object) -> ProblemResponse:
+def fallback_not_found(_: str) -> ProblemResponse:
     """
     If you can't find a matching API endpoint, fallback to returning a 404.