The `replaced_task_nesting` ([docs](https://docs.celeryq.dev/en/stable/userguide/tasks.html#task-request) @ `New in version 5.2.` ) was missing from the `request` because it wasn't parsed correctly over the call stack. This made the whole feature invalid as you always lost the `replaced_task_nesting` value which made it reset to zero.

This PR fixes the handling of `replaced_task_nesting` and also adds integration tests for the feature that didn't exist before.
Fixed replaced_task_nesting. The `replaced_task_nesting` ([docs](https://docs.celeryq.dev/en/stable/userguide/tasks.html#task-request) @ `New in version 5.2.` ) was missing from the `request` because it wasn't parsed correctly over the call stack. This made the whole feature invalid as you always lost the `replaced_task_nesting` value which made it reset to zero.

This PR fixes the handling of `replaced_task_nesting` and also adds integration tests for the feature that didn't exist before.