Fix failures for Projects::AutocompleteSourcesController#epics

What does this MR do and why?

Fix failing request when project has no group

We are observing failures for the endpoint Projects::AutocompleteSourcesController#epics for calling project.group.licensed_feature_available?(:epics) because the project's group can be nil.

Logs: https://log.gprd.gitlab.net/app/r/s/OFvD7 (internal)

References

&16498

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.