fix deprecation warning by making the regex a raw string

Author: Zsailer

jupyter_server/auth/login.py

@@ -109,7 +109,7 @@ def set_login_cookie(cls, handler, user_id=None):
         handler.set_secure_cookie(handler.cookie_name, user_id, **cookie_options)
         return user_id
 
-    auth_header_pat = re.compile("token\s+(.+)", re.IGNORECASE)
+    auth_header_pat = re.compile(r"token\s+(.+)", re.IGNORECASE)
 
     @classmethod
     def get_token(cls, handler):