rust-url treats a trailing 'C:'/'C|' path segment as a Windows drive
letter when shortening a path with '..', for every scheme. Per the URL
Standard that exemption only applies to file:. Work around it in the
Rust binding (fix pending upstream in servo/rust-url#1138) so that
new URL('..', 'abc://x/y/z/C:/') resolves to 'abc://x/y/z/'.