Motivation for this change

The git-secret script(s) use gawk. Before this change:

$ nix-env -f ~/code/nixpkgs -iA git-secret # master branch of nixpkgs
installing 'git-secret-0.2.4'
$ git secret init
/nix/store/i5xpjcrjvsh89ckkw470c94561nzw948-git-secret-0.2.4/bin/.git-secret-wrapped: line 129: gawk: command not found
'/home/aiken/code/git-secret-test/.gitsecret/' created.
/nix/store/i5xpjcrjvsh89ckkw470c94561nzw948-git-secret-0.2.4/bin/.git-secret-wrapped: line 254: gawk: command not found

@lo1tuma

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.