docs/zh_CN: reformat zh_CN/dev-tools/testing-overview

Reorganise several long lines in order to satisfy the kernel coding
style.

Signed-off-by: Hu Haowen <src.res@email.cn>
Reviewed-by: Yanteng Si <siyanteng@loongson.cn>
Link: https://lore.kernel.org/r/20210724130611.4231-1-src.res@email.cn


Signed-off-by: Jonathan Corbet <corbet@lwn.net>