Rollup merge of #126223 - jieyouxu:rmake-run-in-tmpdir-self-test, r=Kobzol

run-make: add `run_in_tmpdir` self-test

Add a basic sanity test for `run_in_tmpdir` to make sure that files (including read-only files) and directories created inside the "scratch" tmpdir are removed after the closure returns.

r? ghost (while i run a try job)

try-job: x86_64-msvc

Author: matthiaskrgr