[maint] metainfo: update copyright info
[maint] metainfo: update copyright info

After SPDX approves the GNU All Permissive license, we will
switch the XML metainfo license tag to that license.  Until then
its dual-licensed CC0 and All-Permissive.

See also:
https://github.com/hughsie/appdata-tools#27

catch22/octave-doctest