mate.pluma: 1.20.1 -> 1.21.0

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

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

These checks were done:

- built on NixOS
- ran ‘/nix/store/fb3vkl4s4sx82pld3anv8pfmb5axv05a-pluma-1.21.0/bin/pluma -h’ got 0 exit code
- ran ‘/nix/store/fb3vkl4s4sx82pld3anv8pfmb5axv05a-pluma-1.21.0/bin/pluma --help’ got 0 exit code
- ran ‘/nix/store/fb3vkl4s4sx82pld3anv8pfmb5axv05a-pluma-1.21.0/bin/.pluma-wrapped -h’ got 0 exit code
- ran ‘/nix/store/fb3vkl4s4sx82pld3anv8pfmb5axv05a-pluma-1.21.0/bin/.pluma-wrapped --help’ got 0 exit code
- found 1.21.0 with grep in /nix/store/fb3vkl4s4sx82pld3anv8pfmb5axv05a-pluma-1.21.0
- directory tree listing: https://gist.github.com/82bb4a3eafe7fd90b442f992b51bab3c