Bump celery from 5.4.0 to 5.5.3 in /backend (#4450)

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Marco Acierno <[email protected]>

Author: dependabot[bot]

backend/pyproject.toml

@@ -84,7 +84,7 @@ dependencies = [
     "l18n<2022.0,>=2021.3",
     "wagtail==7.1.2",
     "wagtail-localize==1.10",
-    "celery==5.4.0",
+    "celery==5.5.3",
     "wagtail-headless-preview==0.8.0",
     "Jinja2>=3.1.3",
     "icalendar>=5.0.11",