revert wrong fix

Author: adriangb

instrumentation/opentelemetry-instrumentation-django/src/opentelemetry/instrumentation/django/middleware/otel_middleware.py

@@ -352,7 +352,7 @@ def process_response(self, request, response):
 
                     custom_res_attributes = (
                         asgi_collect_custom_headers_attributes(
-                            {'headers': custom_headers},
+                            custom_headers,
                             SanitizeValue(
                                 get_custom_headers(
                                     OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SANITIZE_FIELDS