Forbid ticket owners/reports from changing the triage stage of the own ticket

[alexgmin]

Based on a conversation with @sarahboyce a ticket should never be able to be set as "Accepted" or "Ready for checkin" by the person that created the ticket or the person that is currently assigned to that ticket.

This prevents people from creating a ticket and marking it as accepted, since a different person is supposed to do that.

An option to maybe consider is this permission does not apply to some user roles, in case a Fellow or someone may (but shouldn't) need to do that in a rare case.

Based on my search Trac by default doesn't easily support this, however it may be possible with a custom plugin that adds a PermissionPolicy, as commented here https://groups.google.com/g/trac-users/c/T-bb2GAvqxI/m/tFs0_7yQDAAJ

Whether this is worth the effort is a different topic.