chore: upgrade mypy

As a consequence, we need to resolve a typing issue.

requirements/base.txt

@@ -26,7 +26,7 @@ kubernetes==18.20.0
     # via -r requirements/base.in
 markupsafe==2.0.1
     # via jinja2
-mypy==0.910
+mypy==0.931
     # via -r requirements/base.in
 mypy-extensions==0.4.3
     # via mypy
@@ -59,7 +59,7 @@ six==1.16.0
     #   google-auth
     #   kubernetes
     #   python-dateutil
-toml==0.10.2
+tomli==2.0.1
     # via mypy
 typing-extensions==3.10.0.2
     # via mypy

tutor/plugins.py

@@ -64,7 +64,7 @@ class BasePlugin:
         command = getattr(obj, "command", None)
         if command is not None:
             assert isinstance(command, click.Command)
-        self.command: click.Command = command
+        self.command: Optional[click.Command] = command
 
     @staticmethod
     def load_config(obj: Any, plugin_name: str) -> Dict[str, Config]: