scarab: Add test

[l0b0]

Description of changes

Simple verification that Scarab runs at all, to avoid regressions like #345038.

I can't find documentation about any CLI flags being supported by Scarab, so worst case scenario this will have to be expanded to a full-on GUI test to make sure the program works.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[huantianad]

ngl I'm not too familiar with nix test conventions haha, I'll check later more

Are we now sorting arguments alphabetically? I thought we sorted them by first usage... I have no idea where this convention is defined though.

We should probably set

projectFile = "Scarab/Scarab.csproj";
testProjectFile = "Scarab.Tests/Scarab.Tests.csproj";

to stop including the unit tests in the release build and also set

doCheck = true;

to actually run the unit tests, in a separate commit.