Prevent the only remaining team owner to change their role to member

[gtsiolis]

Bug description

While we are now preventing the last team owner to leave a team (see #4623), we're not preventing the only remaining team owner to change their role to member, leading edge cases like member-less teams after leaving the team (#6311) or owner-less teams.

See also relevant discussion (internal). Cc @ jimmybrancaccio @jldec

Cc @nidhinmanu because #6311 (comment)

From another relevant discussion:

The last owner can’t leave a team, but can change to a member and then leave.

Steps to reproduce

1. Create a team
2. Change your role to member
3. Leave a team
4. Try creating a new team with the same name ❗

Workspace affected

No response

Expected behavior

No response

Example repository

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Anything else?

No response

Front conversations

[gtsiolis]

A user run into this issue in #13635.
Looping in @geropl and @jldec in case this is worth prioritizing.

[easyCZ]

• [server] Disallow removing all Owners from a team #13744