### 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
-7.647086,
        -8.165343,
        -8.277936,
        -8.156116,
        -8.104215,
        -8.45849,
        -8.249917,
        -2.0896196,
        -0.67172474 };
    private static final double[] END_TOKEN_SCORES = new double[] {
        1.0593028,
        -8.276232,
        -7.9352865,
        -8.340191,
        -8.326643,
        -8.225507,
        -8.548992,
        -8.50256,
        -8.716394,
        -8.0558195,
        -8.4110565,
        -6.564298,
        -8.570332,
        .01,
        -7.2465587,
        .6000237,
        -8.045577,
        -6.3548584,
        -3.5642238 };