Investigate failing tests (ffmpeg and lighttpd)

[terriko]

In #579 I disabled two tests:

                    pytest.param(
                        "http://archive.ubuntu.com/ubuntu/pool/universe/f/ffmpeg/",
                        "ffmpeg_4.1.1-1_amd64.deb",
                        "ffmpeg",
                        "4.1.1",
                        marks=pytest.mark.xfail(reason="File cannot be downloaded"),
                    ),
...
                    (
                    pytest.param(
                        "https://download-ib01.fedoraproject.org/pub/epel/8/Everything/x86_64/Packages/l/",
                        "lighttpd-1.4.55-1.el8.x86_64.rpm",
                        "lighttpd",
                        "1.4.55",
                        marks=pytest.mark.xfail(reason="File won't download on github"),
                    ),

(you can find them by searching for 'xfail' in test_scanner too)

lighttpd works on my local machine, so may be a transient network problem (is github actions being rate limited by fedoraproject.org?) but ffmpeg doesn't work for me locally so we may need to replace that test.