fix ch07 unit test (#470)

ch07/01_main-chapter-code/tests.py

@@ -10,7 +10,7 @@ import subprocess
 
 
 def test_gpt_class_finetune():
-    command = ["python", "ch06/01_main-chapter-code/gpt_class_finetune.py", "--test_mode"]
+    command = ["python", "ch07/01_main-chapter-code/gpt_instruction_finetuning.py", "--test_mode"]
 
     result = subprocess.run(command, capture_output=True, text=True)
     assert result.returncode == 0, f"Script exited with errors: {result.stderr}"