Bump celery 5.5.3 -> 5.6.3

- Dependency update: bug fixes including Redis reconnect after failover,
  Django worker recursion fix, eventlet warm shutdown fix, chord O(K²)
  message bloat fix. No breaking changes.
- kombu also bumped 5.5.4 -> 5.6.2 as a transitive dependency.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Author: rayharnett

pyproject.toml

@@ -37,7 +37,7 @@ dependencies = [
     "attrs~=25.4.0",
     "boto3==1.41.2",
     "celery-redis-cluster~=0.2.3",
-    "celery==5.5.3",
+    "celery==5.6.3",
     "certifi==2024.8.30",
     "click-repl~=0.3.0",
     "click==8.1.8",