Add CI support for EL9
This MR adds CI pipeline for EL9 (Rocky Linux 9).
Maintenance will be performed on git.ligo.org, containers.ligo.org, and docs.ligo.org on Tuesday 18 February 2025 starting at approximately 9am MST (4pm UTC, 8am PST). It is expected to take around 30 minutes and there will be several periods of downtime throughout the maintenance. Please address any comments, concerns, or questions to the helpdesk.
This MR adds CI pipeline for EL9 (Rocky Linux 9).