Fix Celery custom header propagation without tracing

Author: cursoragent

sentry_sdk/integrations/celery/__init__.py

@@ -231,11 +231,11 @@ def _update_celery_task_headers(
                 if key.startswith("sentry-"):
                     updated_headers["headers"][key] = value
 
-            # Preserve user-provided custom headers in the inner "headers" dict
-            # so they survive to task.request.headers on the worker (celery#4875).
-            for key, value in original_headers.items():
-                if key != "headers" and key not in updated_headers["headers"]:
-                    updated_headers["headers"][key] = value
+        # Preserve user-provided custom headers in the inner "headers" dict
+        # so they survive to task.request.headers on the worker (celery#4875).
+        for key, value in original_headers.items():
+            if key != "headers":
+                updated_headers.setdefault("headers", {}).setdefault(key, value)
 
     return updated_headers