tests/functional/check-refs.nix: format newly added test

(cherry picked from commit 4d72e0f)

Author: trofi

tests/functional/check-refs.nix

@@ -81,8 +81,11 @@ rec {
 
   test12 = makeTest 12 {
     builder = builtins.toFile "builder.sh" "mkdir $out $lib";
-    outputs = ["out" "lib"];
-    disallowedReferences = ["dev"];
+    outputs = [
+      "out"
+      "lib"
+    ];
+    disallowedReferences = [ "dev" ];
   };
 
 }