Change github app startup logic to support gunicorj

pr_agent/servers/github_app.py

@@ -280,7 +280,6 @@ async def root():
     return {"status": "ok"}
 
 
-def start():
 if get_settings().github_app.override_deployment_type:
     # Override the deployment type to app
     get_settings().set("GITHUB.DEPLOYMENT_TYPE", "app")
@@ -289,8 +288,7 @@ def start():
 app = FastAPI(middleware=middleware)
 app.include_router(router)
 
+
+def start():
     uvicorn.run(app, host="0.0.0.0", port=int(os.environ.get("PORT", "3000")))
 
-
-if __name__ == '__main__':
-    start()