mpage: 2.5.6 -> 2.5.7 (#42689)

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

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

These checks were done:

- built on NixOS
- /nix/store/27fvqzw0vgbjadl2ngwggsz2gs3m4a15-mpage-2.5.7/bin/mpage passed the binary check.
- 1 of 1 passed binary check by having a zero exit code.
- 0 of 1 passed binary check by having the new version present in output.
- found 2.5.7 with grep in /nix/store/27fvqzw0vgbjadl2ngwggsz2gs3m4a15-mpage-2.5.7
- directory tree listing: https://gist.github.com/7deed27eaf23f2578d5dfcb1005b1a0c
- du listing: https://gist.github.com/e1cafa83fbe346375875854bf40a6057