`add_collection()` is missing the `ModuleType` in the type-hints

[exhuma]

Since upgrading to 2.1.2 I'm getting a typing error when adding a module as collection.

The error originates from this line: https://github.com/pyinvoke/invoke/blob/b2da4d929d0e895d44d7f5b4581749f4709022e6/invoke/collection.py#L287

It can be fixed by using

    def add_collection(
        self,
        coll: Union["Collection", ModuleType],     # <-- fix
        name: Optional[str] = None,
        default: Optional[bool] = None,
    ) -> None:

[kuwv]

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