Add system role to deepseek chat template

[AllentDan]

No description provided.

[lvhan028]

model = MODELS.get('deepseek')()
messages = [{
    'role': 'system',
    'content': 'you are a helpful assistant'
}, {
    'role': 'user',
    'content': 'who are you'
}, {
    'role': 'assistant',
    'content': 'I am an AI'
}, {
    'role': 'user',
    'content': 'hi'
}]
from transformers import AutoTokenizer
tokenizer = AutoTokenizer.from_pretrained(
    'deepseek-ai/DeepSeek-V2-Lite', trust_remote_code=True)
ref = tokenizer.apply_chat_template(messages, tokenize=False)
res = '<｜begin▁of▁sentence｜>' + model.messages2prompt(messages)
assert res.startswith(ref)

It tests failed using the above case.

[AllentDan]

But in real testing, 'who are you' should be responsed with ' I am an AI'

[lvhan028]

Can we add UTs to cover ti?

[RunningLeon]

LGTM

[lvhan028]

[:-1] should be removed