projects/transfer: improve permission error message
What does this MR do?
Improve the error message when the transfer of a project into another namespace fails because of insufficient permissions.
The error message could probably be further improved, but #27843 has been opened for 2+ years already and I just tripped on this issue today, so I think this is a good start
Closes #27843
Note: this MR will require changes to the translations, and I have no idea what the procedure is for that.
Does this MR meet the acceptance criteria?
Availability and Testing
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I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)