It does not like dynamically defined attributes, unsurprisingly

It looks *modern*!

Since this is a privacy sensitive action, a short message is now
displayed on first run.

This reverts commit bde9b311.

This will be used by some package managers to display information about
poezio.

Use `flatpak-builder build-dir io.poez.Poezio.json` to build it in
build-dir, and `flatpak-builder --run build-dir io.poez.Poezio.json
poezio` to test it.

Note that poezio will still be downloaded from its repository, rather
than built from the local clone.