Fallback to group's owners/masters when a project has none for the "access requested email"

What does this MR do?

From b31c5052:

Fallback to group's owners/masters when a project has none

A project in a group can have no explicit owners/masters,
in that case we fallbacks to the group's owners/masters.

Are there points in the code the reviewer needs to double check?

No.

Why was this MR needed?

Because of #18757 (closed).

What are the relevant issue numbers?

Fixes #18757 (closed).

Does this MR meet the acceptance criteria?

• No need for CHANGELOG.
• No need for documentation.
• No API support added.
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together