mate.mate-system-monitor: 1.20.0 -> 1.20.1

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-system-monitor/versions.

These checks were done:

- built on NixOS
- /nix/store/x5i2inxsxs4jcjqhsn3mv94lsdxmr3g7-mate-system-monitor-1.20.1/bin/mate-system-monitor passed the binary check.
- /nix/store/x5i2inxsxs4jcjqhsn3mv94lsdxmr3g7-mate-system-monitor-1.20.1/bin/.mate-system-monitor-wrapped passed the binary check.
- 2 of 2 passed binary check by having a zero exit code.
- 0 of 2 passed binary check by having the new version present in output.
- found 1.20.1 with grep in /nix/store/x5i2inxsxs4jcjqhsn3mv94lsdxmr3g7-mate-system-monitor-1.20.1
- directory tree listing: https://gist.github.com/a4cdb9b1bfcf5b27047a4f9635faa789
- du listing: https://gist.github.com/1a05da069ac7049838de573c089699de