Fix missing spaces in system prompt of Llama2 tokenizer
# What does this PR do?

This PR fixes a typo  in system prompt of Llama2 tokenizer. There are missing spaces compared to https://github.com/facebookresearch/llama/blob/main/llama/generation.py

Thank you.
cc @ArthurZucker <|||||>Hey thanks, a similar PR is also #24935. Same comment would apply here, make sure `make style` is green and should be good! <|||||>Hi, thank you so much for your help. Seems it still cannot go green. I am not very familiar with it ... Could you give me some guidance? ;)<|||||>_The documentation is not available anymore as the PR was closed or merged._