Support Ubuntu Impish

[jgcodes2020]

Apparently that support was reverted, I suppose this issue can be used to track.

[duckimann]

The script still works fine at that version... unless you upgrade the distro 😂 The script uses the backup from the old distro to generate the gresource file for the new distro and in this case, the CSS in the hirsute distro is different from the one that comes with impish thus causing the error.

In fact, I did try to fix it (my PR was 18d ago) and seems like @thiggy01 doesn't online that frequently.