Use tagged union for getaddrinfo()

[Dreamsorcerer]

Fixes our regression: #15788 (comment)
Should also fix the pre-existing ignore too.

[github-actions]

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

urllib3 (https://github.com/urllib3/urllib3)
+ test/contrib/test_socks.py:120: error: Incompatible return value type (got "list[tuple[Literal[AddressFamily.AF_INET], SocketKind, int, str, tuple[str, int]] | tuple[Literal[AddressFamily.AF_INET6], SocketKind, int, str, tuple[str, int, int, int] | tuple[int, bytes]]]", expected "list[tuple[AddressFamily, SocketKind, int, str, tuple[str, int] | tuple[str, int, int, int] | tuple[int, bytes]]]")  [return-value]
+ test/contrib/test_socks.py:120: note: "list" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance
+ test/contrib/test_socks.py:120: note: Consider using "Sequence" instead, which is covariant

trio (https://github.com/python-trio/trio)
+ src/trio/_socket.py:218: error: Incompatible return value type (got "list[tuple[Literal[AddressFamily.AF_INET], SocketKind, int, str, tuple[str, int]] | tuple[Literal[AddressFamily.AF_INET6], SocketKind, int, str, tuple[str, int, int, int] | tuple[int, bytes]]]", expected "list[tuple[AddressFamily, SocketKind, int, str, tuple[str, int] | tuple[str, int, int, int] | tuple[int, bytes]]]")  [return-value]
+ src/trio/_socket.py:218: note: "list" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance
+ src/trio/_socket.py:218: note: Consider using "Sequence" instead, which is covariant
+ src/trio/_socket.py:247: error: Argument 1 to "to_thread_run_sync" has incompatible type "Callable[[bytes | str | None, bytes | str | int | None, int, int, int, int], list[tuple[Literal[AddressFamily.AF_INET], SocketKind, int, str, tuple[str, int]] | tuple[Literal[AddressFamily.AF_INET6], SocketKind, int, str, tuple[str, int, int, int] | tuple[int, bytes]]]]"; expected "Callable[[bytes | None, bytes | str | int | None, int, int, int, int], list[tuple[AddressFamily, SocketKind, int, str, tuple[str, int] | tuple[str, int, int, int] | tuple[int, bytes]]]]"  [arg-type]
+ src/trio/_tests/test_socket.py:128: error: Argument 1 to "MonkeypatchedGAI" has incompatible type "Callable[[bytes | str | None, bytes | str | int | None, int, int, int, int], list[tuple[Literal[AddressFamily.AF_INET], SocketKind, int, str, tuple[str, int]] | tuple[Literal[AddressFamily.AF_INET6], SocketKind, int, str, tuple[str, int, int, int] | tuple[int, bytes]]]]"; expected "Callable[[str | bytes | None, str | bytes | int | None, int, int, int, int], list[tuple[AddressFamily, SocketKind, int, str, tuple[str, int] | tuple[str, int, int, int] | tuple[int, bytes]]]]"  [arg-type]

mongo-python-driver (https://github.com/mongodb/mongo-python-driver)
+ pymongo/synchronous/helpers.py:135: error: Incompatible return value type (got "list[tuple[Literal[AddressFamily.AF_INET], SocketKind, int, str, tuple[str, int]] | tuple[Literal[AddressFamily.AF_INET6], SocketKind, int, str, tuple[str, int, int, int] | tuple[int, bytes]]]", expected "list[tuple[AddressFamily, SocketKind, int, str, tuple[str, int] | tuple[str, int, int, int] | tuple[int, bytes]]]")  [return-value]
+ pymongo/synchronous/helpers.py:135: note: "list" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance
+ pymongo/synchronous/helpers.py:135: note: Consider using "Sequence" instead, which is covariant
+ pymongo/asynchronous/helpers.py:135: error: Incompatible return value type (got "list[tuple[Literal[AddressFamily.AF_INET], SocketKind, int, str, tuple[str, int]] | tuple[Literal[AddressFamily.AF_INET6], SocketKind, int, str, tuple[str, int, int, int] | tuple[int, bytes]]]", expected "list[tuple[AddressFamily, SocketKind, int, str, tuple[str, int] | tuple[str, int, int, int] | tuple[int, bytes]]]")  [return-value]
+ pymongo/asynchronous/helpers.py:135: note: "list" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance
+ pymongo/asynchronous/helpers.py:135: note: Consider using "Sequence" instead, which is covariant

[srittau]

Looking at the primer hits: return types need an update, which is easier now with the type alias.