[Bug] Inviting members to a project does not show custom roles in role dropdown

In a project, when inviting members to the project, a modal is shown:

Invite buttons	Invite members modal

The role dropdown is not showing custom roles when custom roles are added to the system. We should fix this bug so that custom roles are shown.

Implementation plan

1. Fix role dropdown not showing custom roles for invite members modal.
2. Add feature specs to prevent this from slipping through again.