[OSS Vizier] Tag set_priors in gp_bandit.py to allow experimental overrides.

PiperOrigin-RevId: 553931922

Author: vizier-team

vizier/_src/algorithms/designers/gp_bandit.py

@@ -209,6 +209,7 @@ def update(
     del all_active
     self._trials.extend(copy.deepcopy(completed.trials))
 
+  @_experimental_override_allowed
   def set_priors(self, prior_studies: Sequence[vza.CompletedTrials]) -> None:
     """Updates the list of prior studies for transfer learning.