Fix gsm8k_platinum description

[fxmarty-amd]

As per title, this is in the same line as #2924. We prompt the model with previous examples, but actually not give any instruction to answer the last question / follow the format of example answers, this is not great.

I take inspiration from

lm-evaluation-harness/lm_eval/tasks/gpqa/n_shot/_gpqa_n_shot_yaml

Line 9 in fcddf19

description: "Here are some example questions from experts. Answer the final question yourself, following the format of the previous questions exactly.\n"

.

The resolves #2707

cc @baberabb

cc @Qubitium FYI, probably interesting to you as well.

For reference, on main:

hf ({'pretrained': '/models/openai_gpt-oss-20b', 'dtype': 'auto', 'chat_template_args': {'reasoning_effort': 'low'}, 'enable_thinking': True, 'think_end_token': 200008}), gen_kwargs: (max_gen_toks=4048), limit: None, num_fewshot: None, batch_size: 16
|    Tasks     |Version|     Filter     |n-shot|  Metric   |   |Value |   |Stderr|
|--------------|------:|----------------|-----:|-----------|---|-----:|---|-----:|
|gsm8k_platinum|      3|flexible-extract|     5|exact_match|↑  |0.8983|±  |0.0087|
|              |       |strict-match    |     5|exact_match|↑  |0.0596|±  |0.0068|

With this PR:

hf ({'pretrained': '/models/openai_gpt-oss-20b', 'dtype': 'auto', 'chat_template_args': {'reasoning_effort': 'low'}, 'enable_thinking': True, 'think_end_token': 200008}), gen_kwargs: (max_gen_toks=4048), limit: None, num_fewshot: None, batch_size: 16
|    Tasks     |Version|     Filter     |n-shot|  Metric   |   |Value |   |Stderr|
|--------------|------:|----------------|-----:|-----------|---|-----:|---|-----:|
|gsm8k_platinum|      3|flexible-extract|     5|exact_match|↑  |0.9404|±  |0.0068|
|              |       |strict-match    |     5|exact_match|↑  |0.7072|±  |0.0131|

[Qubitium]

@fxmarty-amd @baberabb We have tested this and validated that it does fix accuracy issues (elevated scores).

[fxmarty-amd]

@Qubitium That's great! Which model did you test on?