crabfit-frontend: change tests to attrset

pkgs/by-name/cr/crabfit-frontend/package.nix

···
     ln -s /var/cache/crabfit $out/standalone/.next/cache
   '';
 
-  passthru.tests = [ nixosTests.crabfit ];
+  passthru.tests = {
+    inherit (nixosTests) crabfit;
+  };
 
   meta = {
     description = "Enter your availability to find a time that works for everyone";