pending mate upgrade patches to 1.26

[Andy Tai]

Hi, I submitted patches to update the Mate desktop to 1.26.

The state of them is that there are two prerequisites that have passed
Guix QA check:

https://issues.guix.gnu.org/64001
https://issues.guix.gnu.org/64012

and the mate upgrade patches are in
https://issues.guix.gnu.org/64084

which Guix QA cannot build-check for now because the first two
dependencies are not merged.

These issues are properly marked in debbugs with "block" relationship.

This may not be clear from looking at the patch issues themselves so I
post a message here. Thanks for reviews and git commits if no issues