fix(pass_through_endpoints.py): use data instead of json for passthrough requests

fixes bedrock latency issue

litellm/proxy/pass_through_endpoints/pass_through_endpoints.py

@@ -383,7 +383,7 @@ class HttpPassThroughEndpointHelpers(BasePassthroughUtils):
                 url=url,
                 headers=headers,
                 params=requested_query_params,
-                json=_parsed_body,
+                data=_parsed_body,
             )
         return response