7z test fails with p7zip

When building diffoscope on debian bookworm or guix, both of which have p7zip instead of 7zip, the build fails.

I performed a test bumping the version from 24.05 to 99.05 (would love a more elegant approach, but the hack worked!) to see what version of "7z" it detects:

tests/comparators/test_sevenz.py::test_metadata_diff SKIPPED (requires 7z; try installing 7zip >= 99.05; [64] detected)

The p7zip version of 7z outputs:

7-Zip [64] 16.02 : Copyright (c) 1999-2016 Igor Pavlov : 2016-05-21

The "[64]" apparently confuses the version detection... obviously this should detect "16.02".

"[64]" is apparently greater than "24.05" in python, so we end up with the test being run even though the version dependency is not met, and it unsurprisingly fails...