replace inaccessible mirror (qt.mirrors.tds.net) in test

[pitkling]

Pull request type

• Bug fix

Which ticket is resolved?

• none, I stumbled upon this when packaging py7zr for NixOS in py7zr: init at 0.22.0; pyppmd: init at 1.1.1; pybcj: init at 1.0.3; multivolumefile: init at 0.2.3; inflate64: init at 1.0.1 NixOS/nixpkgs#384329

What does this PR change?

• fixes a test URL that is no longer accessible