[CQ] remove trailing whitespace from unnecessary_underscores_test source

This *should* be breaking the bots (see: #59867)

Change-Id: I3855954e28e442f189ae9b716a432fc1e1d409fb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/403741
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: pq

pkg/linter/test/rules/unnecessary_underscores_test.dart

@@ -69,15 +69,15 @@ void f(int _, int __) {}
     await assertNoDiagnostics(r'''
 // @dart = 3.6
 
-void f(int _, int __) {} 
+void f(int _, int __) {}
 ''');
   }
 
   test_function_parameter_used() async {
     await assertNoDiagnostics(r'''
 void f(int _, int __) {
   print(__);
-} 
+}
 ''');
   }