buildRustCrate: Fix #60125 - Always set additional env variables during build

[kolloch]

Namely CARGO_PKG_VERSION_PRE and CARGO_PKG_HOMEPAGE
(as cargo does)

@P-E-Meunier

Motivation for this change

The built crate assumes that these environment variables are always set at build time. Cargo does that. Since we are emulating cargo, we should, too.

Things done

I build the crate that failed before using the update nixpkgs.

• 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 nix-review --run "nix-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.

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[P-E-Meunier]

Looks good to me. I just updated the master branch of Carnix, this should be included in the next version.

[dywedir]

Thanks!