CLN: improve is_unique check in Index.intersection (#38154)

Author: phofl

pandas/core/indexes/base.py

@@ -2380,6 +2380,10 @@ def unique(self, level=None):
  """
  if level is not None:
  self._validate_index_level(level)
+
+ if self.is_unique:
+ return self._shallow_copy()
+
  result = super().unique()
  return self._shallow_copy(result)
 
@@ -2866,7 +2870,7 @@ def _intersection(self, other, sort=False):
  result = algos.safe_sort(result)
 
  # Intersection has to be unique
- assert algos.unique(result).shape == result.shape
+ assert Index(result).is_unique
 
  return result