Revert dict.__or__ typeshed change

[ilevkivskyi]

Fixes #21141

I am not sure how typeshed patches work. If possible, I would add some tests here, otherwise I will add tests in a follow-up PR.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

artigraph (https://github.com/artigraph/artigraph)
- tests/arti/internal/test_mappings.py:40: error: Unsupported operand types for | ("dict[str, int]" and "frozendict[Never, int]")  [operator]
+ tests/arti/internal/test_mappings.py:40: error: No overload variant of "__or__" of "dict" matches argument type "frozendict[Never, int]"  [operator]
+ tests/arti/internal/test_mappings.py:40: note: Possible overload variants:
+ tests/arti/internal/test_mappings.py:40: note:     def __or__(self, dict[str, int], /) -> dict[str, int]
+ tests/arti/internal/test_mappings.py:40: note:     def [_T1, _T2] __or__(self, dict[_T1, _T2], /) -> dict[str | _T1, int | _T2]

rotki (https://github.com/rotki/rotki)
- rotkehlchen/chain/evm/decoding/aave/v3/decoder.py:583: error: Unused "type: ignore" comment  [unused-ignore]