Fixed: Incorrect guide message for missing frontend. (#7105)

`{sys.executable} -m pip` -> `{sys.executable} -s -m pip`

https://github.com/comfyanonymous/ComfyUI/pull/7047#issuecomment-2697876793

app/frontend_management.py

@@ -23,7 +23,7 @@ try:
 except ImportError:
     # TODO: Remove the check after roll out of 0.3.16
     req_path = os.path.abspath(os.path.join(os.path.dirname(__file__), '..', 'requirements.txt'))
-    logging.error(f"\n\n********** ERROR ***********\n\ncomfyui-frontend-package is not installed. Please install the updated requirements.txt file by running:\n{sys.executable} -m pip install -r {req_path}\n\nThis error is happening because the ComfyUI frontend is no longer shipped as part of the main repo but as a pip package instead.\n\nIf you are on the portable package you can run: update\\update_comfyui.bat to solve this problem\n********** ERROR **********\n")
+    logging.error(f"\n\n********** ERROR ***********\n\ncomfyui-frontend-package is not installed. Please install the updated requirements.txt file by running:\n{sys.executable} -s -m pip install -r {req_path}\n\nThis error is happening because the ComfyUI frontend is no longer shipped as part of the main repo but as a pip package instead.\n\nIf you are on the portable package you can run: update\\update_comfyui.bat to solve this problem\n********** ERROR **********\n")
     exit(-1)