`os.chmod` is missing validation for `dir_fd` and `follow_symlinks` when `path` is a file descriptor

Bug report

Bug description:

The documentation for os.chmod says it is not correct to use dir_fd or follow_symlinks when path is an open file descriptor...

https://github.com/python/cpython/blob/f74cdf80a120649e4c353430da8cbd1305c00993/Modules/posixmodule.c#L4092-L4095

... but os_chmod_impl never checks it.

When path->is_fd is true it takes the fchmod path and returns success, so both keywords are ignored altogether:

https://github.com/python/cpython/blob/f74cdf80a120649e4c353430da8cbd1305c00993/Modules/posixmodule.c#L4146-L4149

Other os utils (I checked os.stat, os.chown, and os.utime) reject this combination with dir_fd_and_fd_invalid / fd_and_follow_symlinks_invalid before the syscall. os.chown for example:

https://github.com/python/cpython/blob/f74cdf80a120649e4c353430da8cbd1305c00993/Modules/posixmodule.c#L4548-L4550

(The Windows path also has the same problem with: path->is_fd going directly to win32_fchmod.)

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Linked PRs

• gh-156265

Start in Modules/posixmodule.c at os_chmod_impl and inspect the path->is_fd branches for POSIX and Windows. Compare their handling with the validation used by os.chown, os.stat, and os.utime. Done means invalid dir_fd and follow_symlinks combinations are rejected when path is a file descriptor, with behavior covered by the relevant os tests.