nq_open: move multi_target to `exact_match`

lm_eval/tasks/nq_open/README.md

@@ -24,3 +24,6 @@ journal	= {Transactions of the Association of Computational Linguistics}}
 ### Tasks
 
 * `nq_open`
+
+### Changelog
+* 2025-07-21: Added `multi_target` to `exact_match`. Scores should not change.

lm_eval/tasks/nq_open/nq_open.yaml

 task: nq_open
-dataset_path: nq_open
+dataset_path: google-research-datasets/nq_open
 output_type: generate_until
 training_split: train
 validation_split: validation
 description: "Answer these questions:\n\n"
 doc_to_text: "Q: {{question}}?\nA:"
-doc_to_target: "{{answer}}" # TODO: should be multi-target
+doc_to_target: "{{answer}}"
 fewshot_delimiter: "\n"
 generation_kwargs:
   until:
@@ -28,5 +28,6 @@ metric_list:
     ignore_punctuation: true
     regexes_to_ignore:
     - "\\b(?:The |the |An |A |The |a |an )"
+    multi_target: true
 metadata:
   version: 4.0