GH-128520: pathlib ABCs: tweak protocol for virtual path strings (#134104)

Adjust `pathlib._os.vfspath()` so that it doesn't try `os.fsdecode()`. I
don't know that supporting `os.PathLike` arguments is a good idea, so
it's best to leave it out for now.

Lib/test/test_pathlib/support/zip_path.py

@@ -334,4 +334,4 @@ class WritableZipPath(_WritablePath):
         zinfo.external_attr = stat.S_IFLNK << 16
         if target_is_directory:
             zinfo.external_attr |= 0x10
-        self.zip_file.writestr(zinfo, vfspath(target))
+        self.zip_file.writestr(zinfo, target)