[megatron] update megatron_args default_val#6252

Jintao-Huang wants to merge 2 commits intomodelscope:mainmodelscope/ms-swift:mainfrom

Jintao-Huang:update_megatron_args_default_valJintao-Huang/llmscope:update_megatron_args_default_valCopy head branch name to clipboard