scarab: fix crash (NixOS#345038), don't bundle tests

By using testProjectFile, we can properly build the test and run it in
checkPhase, as well as not include the test in the derivation output.

This also happens to fix the startup crash as described in NixOS#345038.

pkgs/tools/games/scarab/default.nix

@@ -23,7 +23,8 @@ buildDotnetModule rec {
   };
 
   nugetDeps = ./deps.nix;
-  projectFile = "Scarab.sln";
+  projectFile = "Scarab/Scarab.csproj";
+  testProjectFile = "Scarab.Tests/Scarab.Tests.csproj";
   executables = [ "Scarab" ];
 
   preConfigureNuGet = ''
@@ -48,6 +49,8 @@ buildDotnetModule rec {
     wrapGAppsHook3
   ];
 
+  doCheck = true;
+
   postFixup = ''
     # Icons for the desktop file
     icotool -x $src/Scarab/Assets/omegamaggotprime.ico