Improve mypy daemon documentation note about local partial types (#16782

)

The existing documentation almost makes it seem like the user has the
option to toggle this.

docs/source/mypy_daemon.rst

@@ -61,7 +61,7 @@ you have a large codebase.)
 
 .. note::
 
-    The mypy daemon automatically enables ``--local-partial-types`` by default.
+    The mypy daemon requires ``--local-partial-types`` and automatically enables it.
 
 
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