Hide type error on one line

> app.py:573: error: "AppContext" has no attribute "setdefault"

This is a workaround for a type bug introduced in Flask 2.0.0 (already
fixed in pallets/flask#4042 [1], but 2.0.1 not yet released).

[1]: pallets/flask#4042

app.py

@@ -570,7 +570,7 @@ def edit_token(session: mwapi.Session) -> str:
     Not to be confused with csrf_token,
     which gets a token for use within the tool."""
 
-    edit_tokens = flask.g.setdefault('edit_tokens', {})
+    edit_tokens = flask.g.setdefault('edit_tokens', {})  # type: ignore
     key = session.host
     if key in edit_tokens:
         return edit_tokens[key]