Rollup merge of #68097 - MikailBag:master, r=shepmaster
Rollup merge of #68097 - MikailBag:master, r=shepmaster

Specify units for test timeout environment variables

I think it is not obvious (I got it from reading libtest sources), so it is worth mentioning in docs.

graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust