adjust test

Calling exclude before saving means that the class is extern on the next iteration, and thus not generated.

tests/misc/java/projects/Issue10280/Main.hx

@@ -29,12 +29,11 @@ class OldClass {
 					public function new() {}
 				}
 			);
-
-			Compiler.exclude('OldClass');
-
 			defined = true;
 		});
 
+		Context.onGenerate(_ -> Compiler.exclude('OldClass'));
+
 		return null;
 	}
 }