Fixes member_approval factory association

What does this MR do and why?

Context

While using the factory for GitlabSubscriptions::MemberManagement::MemberApproval, we observed a mismatch between:

• member_approval.member_namespace_id
• and member_approval.member.member_namespace_id

when we created the factory like FactoryBot.create(:gitlab_subscription_member_management_member_approval), or even when we did FactoryBot.create(:gitlab_subscription_member_management_member_approval, member_namespace: grp) the member_namespace of the member object does not match with the member_namespace of the member_approval.

Problem

The factory did not ensure that the member created belongs to the same member_namespace that was passed (or built). As a result:

• The member_namespace of the associated member could differ from the member_namespace on the MemberApproval itself.
• This caused confusing test behavior and potential false positives in tests relying on this association.

What This MR Does

• Aligns the created member's namespace with the provided (or generated) member_namespace.
• Adds logic to ensure:
  • If member_namespace is a ProjectNamespace, the member is a project_member of that project.
  • If it’s a Group, the member is a group_member of that group.
• Adds a fallback in after(:build) to automatically align member_namespace to the namespace of the created member if one wasn't explicitly passed.

References

#475095 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

• In rails console, run

   m = FactoryBot.create(:gitlab_subscription_member_management_member_approval)
   # or
   grp = FactoryBot.create(:group)
   m = FactoryBot.create(:gitlab_subscription_member_management_member_approval, member_namespace: grp)

• Verify m.member.member_namespace is same as m.member_namespace
• Verify that on master, ^ is not the case.

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