Look for VCS schemes in the URL.

    Returns the matched VCS scheme, or None if there's no match.

def _match_vcs_scheme(url):
    # type: (str) -> Optional[str]
    """Look for VCS schemes in the URL.

    Returns the matched VCS scheme, or None if there's no match.
    """
    from pipenv.patched.notpip._internal.vcs import VcsSupport
    for scheme in VcsSupport.schemes:
        if url.lower().startswith(scheme) and url[len(scheme)] in '+:':
            return scheme
    return None