[3.12] GH-110488: Fix two small issues in `pathlib.PurePath.with_name()` (GH-110651) (#110678)

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 b5f7777cb3ecae02d49e0b348968c1ff1ffe21f4)