Fix RefResolver store parameter type in jsonschema stubs

[sedat4ras]

Fixes #8662

Changes

In stubs/jsonschema/jsonschema/validators.pyi, the store parameter of RefResolver.__init__ was typed as SupportsKeysAndGetItem[str, str] | Iterable[tuple[str, str]], but the actual runtime implementation accepts a mapping/iterable of Mapping[str, Any] (i.e., full JSON schema objects), not plain str values.

The jsonschema source code uses URIDict (which inherits from MutableMapping[str, Any]) for the store, and the store values are schema documents (JSON objects), not strings.

Before:

store: SupportsKeysAndGetItem[str, str] | Iterable[tuple[str, str]] = ...,

After:

store: SupportsKeysAndGetItem[str, Mapping[str, Any]] | Iterable[tuple[str, Mapping[str, Any]]] = ...,

This matches the actual usage pattern where users pass schema documents as store values:

RefResolver("http://example.com/", schema, store={"http://example.com/other": other_schema})

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉