The pre-task validation in apiSnapshotsUpdate was incorrectly rejecting
PUT requests that set the Name to the snapshot's current name. This caused
a 409 response before creating a task, which broke the system test
SnapshotsAPITestCreateUpdate that expects a task to be created and then
fail inside the task.
The fix restores the 'b.Name != name' condition in the pre-task check so
that same-name updates pass through to the task, where the in-task
duplicate check will properly fail them (returning a failed task state
instead of a direct 409).