Remove usage of days_ago() from test suite #23233
Description
Body
days_ago() is deprecated #21653
There are many test using this function thus raising warnings.
This task is to replace all usages of days_ago() in the tests with alternatives.
A stale PR that started to work on it #21830 but didn't finish
Committer
- I acknowledge that I am a maintainer/committer of the Apache Airflow project.