Fix the format of mgsm zh and ja.

[timturing]

This is discussed in #2578 .

[CLAassistant]

All committers have signed the CLA.

[baberabb]

LGTM! could you sign the CLA, if you're willing. We can't merge without without that.

[timturing]

Thanks for the review and sorry for missing the CLA earlier! I've signed it now. Please let me know if there's anything else needed.

[baberabb]

Looks great! closes #2578

[baberabb]

@timturing one last thing. i cant seem to edit the PR. Could you increment the versions in direct_yaml, native_cot/cot_yaml and en_cot/cot_yaml and add a change-log like below to the readme

# changelog
- (en_cot, direct) ver 3; (native_cot) ver 4: issue #2578; PR #2587
  - fix fewshot format: Changed inconsistent usage of ':' (ASCII) and '：' (Chinese) to use '：' consistently.