### Elasticsearch Version

8.9.0

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

any

### Problem Description

If the context text supplied to the Question Answering task is longer than the model's `max_sequence_length` and `truncate` is set to `none` then inference on the model fails with the message:

```
status_exception: question answering result has invalid dimension, expected 2 found [6] 
```
<img width="1438" alt="Screenshot 2023-07-25 at 08 21 37" src="https://github.com/elastic/elasticsearch/assets/2353640/12d296f6-03b2-4cda-89ce-7399348c4104">


### Steps to Reproduce

Use long input text to the question answering task


### Work Aroundf
The fix is to truncate the context which unfortunately may remove the part of the document containing the answer. For reference the call is documented here

```
POST _ml/trained_models/distilbert-base-cased-distilled-squad/deployment/_infer
{
  "docs":[{ "text_field": "question answering context"}],
  "inference_config": {
    "question_answering": {
      "question": "The question to ask",
      "tokenization": {
        "bert": {
          "truncate": "second",
          "span": -1          
        }
      }
    }
  }
}
````

x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/inference/nlp/QuestionAnsweringProcessorTests.java
assertThat(result.get().endToken(), equalTo(5));
    }
    public void testTopScoresMoreThanOne() {
        int seq2Start = 8;
        int numAnswersToGather = 2;
        QuestionAnsweringProcessor.ScoreAndIndicesPriorityQueue result = new QuestionAnsweringProcessor.ScoreAndIndicesPriorityQueue(2);
        QuestionAnsweringProcessor.topScores(
            START_TOKEN_SCORES,
            END_TOKEN_SCORES,
            numAnswersToGather,
            result::insertWithOverflow,
            seq2Start,
            START_TOKEN_SCORES.length,
            10,
            0
        );
        assertThat(result.size(), equalTo(numAnswersToGather));
        QuestionAnsweringProcessor.ScoreAndIndices[] topScores = new QuestionAnsweringProcessor.ScoreAndIndices[numAnswersToGather];
        for (int i = numAnswersToGather - 1; i >= 0; i--) {
            topScores[i] = result.pop();
        }
        assertThat(topScores[0].score(), closeTo(0.05265336, 1e-6));
        assertThat(topScores[0].startToken(), equalTo(0));
        assertThat(topScores[0].endToken(), equalTo(7));
        assertThat(topScores[1].score(), closeTo(0.0291865, 1e-6));
        assertThat(topScores[1].startToken(), equalTo(0));
        assertThat(topScores[1].endToken(), equalTo(5));
    }
}