chore(deps): bump celery from 5.5.3 to 5.6.0 in /docs

Bumps [celery](https://github.com/celery/celery) from 5.5.3 to 5.6.0.
- [Release notes](https://github.com/celery/celery/releases)
- [Changelog](https://github.com/celery/celery/blob/main/Changelog.rst)
- [Commits](celery/celery@v5.5.3...v5.6.0)

---
updated-dependencies:
- dependency-name: celery
  dependency-version: 5.6.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs/requirements.txt

@@ -1,6 +1,6 @@
 sphinx==8.2.3
 sphinx_rtd_theme==3.0.2
-celery==5.5.3
+celery==5.6.0
 django>=4.2,<6
 structlog
 sphinx-autobuild==2025.8.25