[invoiceninja] Check for new PHP version compatibility

[noave]

PHP 8.0 is EOL and wont soon be available on Uberspace any longer.

Check if this guide works with PHP 8.2 (or at least 8.1) and update it accordingly. Otherwise, if you cannot fix it with the new versions mark the guide as broken like it is described here: https://github.com/Uberspace/lab/blob/main/BROKEN_GUIDES.md

(This issue has been created automatically, the guide might already be up to date, in this case you can just comment and close the issue here)

[rexjohannes]

see https://github.com/Uberspace/lab/issues/850

but it looks like invoiceninja does work generally with php 8.2