type annotation for `{dict_keys,dict_items}.is_disjoint` argument is too narrow

In the PR that added these annotations, @hauntsaninja said:

My instinct is to try it the stricter way and relax it if we ever get a real user complaint about it, but happy to go along with whatever others think is best

I'd like to provide such a complaint. In ty, we would like to infer precise key-type specializations (unions of string literals) of dict_keys and dict_items for closed TypedDicts, where all possible keys are known. We have real user requests for this, because it allows iterating over dict keys/items and passing the keys along to a function that expects a limited set of literals.

But doing this causes false positives with isdisjoint, because the following valid code will now error:

class TD(TypedDict, closed=True):
    x: int

def check(td: TD) -> None:
    # Both operations are safe at runtime but will report invalid-argument-type:
    td.keys().isdisjoint(["other"])
    td.items().isdisjoint([("other", 1)])

This is really a sub-issue of https://github.com/python/typeshed/issues/15271, the same category of issue as #6597.

まず、PR 12309 で導入されたアノテーションと、issue #15271 の関連する議論を確認します。この issue にある 2 つの閉じた TypedDict の例を再現し、その後、正確なキー型とアイテム型を失うことなく両方の有効な呼び出しが受け入れられるように、is_disjoint 引数の型付けを調整します。結果として得られる型チェックの動作を検証します。