mate.libmateweather: 1.20.1 -> 1.21.0 (#43191)

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools.

This update was made based on information from https://repology.org/metapackage/libmateweather/versions.

These checks were done:

- built on NixOS

- 0 of 0 passed binary check by having a zero exit code.
- 0 of 0 passed binary check by having the new version present in output.
- found 1.21.0 with grep in /nix/store/ksayjrqlh72h4lzyqwdwzzr193ygl0xb-libmateweather-1.21.0
- directory tree listing: https://gist.github.com/77147d67fc7b1421588d484ca7a98dec
- du listing: https://gist.github.com/a93673e3e9aba588db3b7595bd49248a