kinit: increase environment limit

[CertainLach]

Motivation for this change

Limit is already increased for standard xorg plasma distribution to
start, but with wayland, even more libraries being added

Increasing this limit to 1 << 20 (1M) seems to be enough (For me
length is 80K), and not so much for regular desktops

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• 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 nixpkgs-review --run "nixpkgs-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)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[oxalica]

🤔 I'm wondering why there need to be a troublesome but increase-able limit. Can we simply throw away the check?

[CertainLach]

@oxalica this check can prevent broken input from being passed to program, so it shouldn't be removed, i think.
Increasing it to 1M should be enough for a long time