Clean up unneeded unique() calls on ORM

### Body

Similar to #43064. Maybe there are more to be had? cc @dstandish

I can find 6 with a naive text search in main, 4 in main and 2 in providers. We should review them individually.

https://github.com/apache/airflow/blob/e20146d44b340f719f7fb432f93741e011690558/airflow/assets/manager.py#L161-L167

https://github.com/apache/airflow/blob/e20146d44b340f719f7fb432f93741e011690558/airflow/dag_processing/collection.py#L64-L75

https://github.com/apache/airflow/blob/e20146d44b340f719f7fb432f93741e011690558/airflow/jobs/scheduler_job_runner.py#L1327-L1338

https://github.com/apache/airflow/blob/e20146d44b340f719f7fb432f93741e011690558/airflow/www/views.py#L1000-L1006

https://github.com/apache/airflow/blob/e20146d44b340f719f7fb432f93741e011690558/providers/src/airflow/providers/fab/auth_manager/api_endpoints/role_and_permission_endpoint.py#L88-L92

https://github.com/apache/airflow/blob/e20146d44b340f719f7fb432f93741e011690558/providers/src/airflow/providers/fab/auth_manager/security_manager/override.py#L2792-L2799

(There is a 7th `unique()` match in a Jinja2 template.)

### Committer

- [X] I acknowledge that I am a maintainer/committer of the Apache Airflow project.

Start with the six linked Python call sites and search for the seventh occurrence in the Jinja2 template. Review each unique() call individually, including the provider files, and run the relevant Airflow tests after each change. Done means only unnecessary calls are removed without changing behavior.

Written by the indexing model from the issue text.