Fix: tf dipole atomic key (#3975)

I believe this should fix #3970 

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Bug Fixes**
- Updated label naming convention from "atomic_" to "atom_" to ensure
consistency in labeling.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

deepmd/tf/loss/tensor.py

@@ -148,7 +148,7 @@ def label_requirement(self) -> List[DataRequirementItem]:
         # data required
         data_requirements.append(
             DataRequirementItem(
-                "atomic_" + self.label_name,
+                "atom_" + self.label_name,
                 self.tensor_size,
                 atomic=True,
                 must=False,