[3.12] pythonGH-110488: Fix two small issues in `pathlib.PurePath.wit…

…h_name()` (pythonGH-110651)

Ensure that `PurePath('foo/a').with_name('.')` raises `ValueError`

Ensure that `PureWindowsPath('foo/a').with_name('a:b')` does not raise
`ValueError`..
(cherry picked from commit b5f7777)

Co-authored-by: Barney Gale <[email protected]>