Update lux

[kfjahnke]

The latest version has a modified AppRun which may help with the creation of a default snapshot during the test of the Appimage

[probonopd]

Related tp #3209.

[kfjahnke]

Let me explain: I checked https://appimage.github.io/lux/ and noticed that it does not offer a download button, and it doesn't link to my work at all. So I rewrote the metadata.xml and put in as much info as I could hoping that the scan would produce some link to my project from, e.g., the URL I include.

While I was at it I thought I could change the AppRun to invoke lux so that your test would get a valid default snapshot.
Initially I got the pull request wrong, trying to go via patch-2 - and I couldn't trigger the test. Then I noticed, at the bottom of https://appimage.github.io/lux/, the link to update it: https://github.com/AppImage/appimage.github.io/blob/master/data/lux. That link resulted in the patch-3 branch and triggered the test, but now even the main test did not come out passed and the snapshot test failed as well.

So I'm a bit at a loss what else to do. Can you give a helpful hint?