fix(app.py): if condition (#12314)

Signed-off-by: -LAN- <laipz8200@outlook.com>

api/app.py

@@ -17,7 +17,7 @@ else:
     # It seems that JetBrains Python debugger does not work well with gevent,
     # so we need to disable gevent in debug mode.
     # If you are using debugpy and set GEVENT_SUPPORT=True, you can debug with gevent.
-    if (flask_debug := os.environ.get("FLASK_DEBUG", "0")) and flask_debug.lower() not in {"false", "0", "no"}:
+    if (flask_debug := os.environ.get("FLASK_DEBUG", "0")) and flask_debug.lower() in {"false", "0", "no"}:
         from gevent import monkey  # type: ignore
 
         # gevent