Fix missing _expected_100_continue attribute in UWSGIRequest

The wsgi.create() function expects req._expected_100_continue but
UWSGIRequest didn't have this attribute, causing an AttributeError.
Set to False since uWSGI runs behind a frontend server that handles
100-continue negotiation.

gunicorn/uwsgi/message.py

@@ -58,6 +58,9 @@ class UWSGIRequest:
         # Proxy protocol compatibility
         self.proxy_protocol_info = None
 
+        # 100-continue: not applicable for uWSGI as the frontend handles this
+        self._expected_100_continue = False
+
         # Check if the source IP is allowed
         self._check_allowed_ip()