Fix another bug when sampling from the data

Author: michalk8

src/ott/neural/data/datasets.py

@@ -95,7 +95,7 @@ def __getitem__(self, ix: int) -> Item_t:
     src = self.src_data[ix]
     src = {f"{self.SRC_PREFIX}_{k}": v for k, v in src.items()}
 
-    tgt = self.src_data[ix] if self.is_aligned else self._sample_from_target(ix)
+    tgt = self.tgt_data[ix] if self.is_aligned else self._sample_from_target(ix)
     tgt = {f"{self.TGT_PREFIX}_{k}": v for k, v in tgt.items()}
 
     return {**src, **tgt}