[tune] Fix an example for _Brackets of async hyperband scheduler (#7538)

python/ray/tune/schedulers/async_hyperband.py

@@ -124,12 +124,12 @@ class _Bracket():
     the correct rung corresponding to the current iteration of the result.
 
     Example:
-        >>> b = _Bracket(1, 10, 2, 3)
+        >>> b = _Bracket(1, 10, 2, 0)
         >>> b.on_result(trial1, 1, 2)  # CONTINUE
         >>> b.on_result(trial2, 1, 4)  # CONTINUE
         >>> b.cutoff(b._rungs[-1][1]) == 3.0  # rungs are reversed
         >>> b.on_result(trial3, 1, 1)  # STOP
-        >>> b.cutoff(b._rungs[0][1]) == 2.0
+        >>> b.cutoff(b._rungs[3][1]) == 2.0
     """
 
     def __init__(self, min_t, max_t, reduction_factor, s):