mate.mate-sensors-applet: 1.20.2 -> 1.21.0 (#43185)

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

This update was made based on information from https://repology.org/metapackage/mate-sensors-applet/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/4l932vamscavmky2lgamncxphnyz3q5h-mate-sensors-applet-1.21.0
- directory tree listing: https://gist.github.com/c35172fcab62bda25f00c14783d252cd
- du listing: https://gist.github.com/458d0a68a4ec6d48c6798976072f2d53