test: render_update_json_installs_the_suppression_guard_around_resolution mutates process PATH, racing tar-spawning tests #650

apps/rocm/src/therock.rs render_update_json_installs_the_suppression_guard_around_resolution sets the process-wide PATH to a single temp directory (std::env::set_var("PATH", &bin_dir)) under PROCESS_ENV_TEST_LOCK. Tests that spawn tar don't take that lock. So under cargo test -p rocm --bin rocm (one process, many threads) they can intermittently fail with failed to launch tar: No such file or directory.

It was seen locally in therock::archive_properties::sdk_tarball_unpack_extracts_a_benign_tarball_into_the_install_root, which passes alone and on re-run. CI's Linux nextest runs one process per test, so it hides this. The Windows lane and the coverage job use cargo test, so they can hit it.

The fix #253 made for the Python-resolver tests applies here too: pass the environment into the code under test as a value instead of mutating the process PATH.

Found while fixing the related fake-executable race in #649.