parse_qsl no longer treats ';' as valid query separator for security
reason because most proxies did not do so and it was possible to poison
proxy cache due to difference in query separator handling (see bugs.python.org/issue42967).

To handle credentials we don't have any proxy here, and it is still
perfectly valid to use ';' as credentials separator.

-> Fix it with ';' -> '&' replace workaround, before feeding credentials
string to parse_qsl.

Amends: b9a42957.