`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:

invoke/invoke/collection.py

Line 287 in b2da4d9

coll: "Collection",

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]

#956