pigz: 2.3.4 -> 2.4

Semi-automatic update. These checks were done:

- built on NixOS
- ran `/nix/store/j8izqqx03n8aqqab57sybxkv483xfz05-pigz-2.4/bin/pigz -h` got 0 exit code
- ran `/nix/store/j8izqqx03n8aqqab57sybxkv483xfz05-pigz-2.4/bin/pigz --help` got 0 exit code
- ran `/nix/store/j8izqqx03n8aqqab57sybxkv483xfz05-pigz-2.4/bin/pigz -V` and found version 2.4
- ran `/nix/store/j8izqqx03n8aqqab57sybxkv483xfz05-pigz-2.4/bin/pigz --version` and found version 2.4
- found 2.4 with grep in /nix/store/j8izqqx03n8aqqab57sybxkv483xfz05-pigz-2.4
- found 2.4 in filename of file in /nix/store/j8izqqx03n8aqqab57sybxkv483xfz05-pigz-2.4