libuv: 1.20.3 -> 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/libuv/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/95msjm8zq3ahka1i7jcllk6kzqa2xxzp-libuv-1.21.0
- directory tree listing: https://gist.github.com/8a2b5bb197a6f9ec0f1e2ba156b359f7
- du listing: https://gist.github.com/ef01d39e12559715d3876f27594aa77f