harfbuzz-icu: 1.7.5 -> 1.7.6

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

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

These checks were done:

- built on NixOS
- Warning: no binary found that responded to help or version flags. (This warning appears even if the package isn't expected to have binaries.)
- found 1.7.6 with grep in /nix/store/9dzws8q45r5sybzlcz8xc9gil9ng0wf6-harfbuzz-icu-1.7.6
- found 1.7.6 in filename of file in /nix/store/9dzws8q45r5sybzlcz8xc9gil9ng0wf6-harfbuzz-icu-1.7.6
- directory tree listing: https://gist.github.com/660379e3d103a344b19913754635a124