tests fail randomly in nix

these tests fail randomly so hydra eventually manages to build shadowenv, but this should really pass first try

❯ nix-build -A shadowenv
error: builder for '/nix/store/a340k0chdxzmlaf996rr1mldb128ibqk-shadowenv-3.0.3.drv' failed with exit code 101;
       last 25 log lines:
       > called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }
       > note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
       >
       > ---- loader::tests::find_shadowenv_paths_using_relative_paths stdout ----
       > thread 'loader::tests::find_shadowenv_paths_using_relative_paths' panicked at src/loader.rs:104:51:
       > called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }
       >
       > ---- loader::tests::find_shadowenv_paths_success stdout ----
       > thread 'loader::tests::find_shadowenv_paths_success' panicked at src/loader.rs:104:51:
       > called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }
       >
       > ---- loader::tests::find_shadowenv_paths_nonexistant_link_target stdout ----
       > thread 'loader::tests::find_shadowenv_paths_nonexistant_link_target' panicked at src/loader.rs:104:51:
       > called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }
       >
       >
       > failures:
       >     loader::tests::find_shadowenv_paths_nonexistant_link_target
       >     loader::tests::find_shadowenv_paths_not_a_symlink
       >     loader::tests::find_shadowenv_paths_success
       >     loader::tests::find_shadowenv_paths_using_relative_paths
       >
       > test result: FAILED(B. 22 passed; 4 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.06s
       >
       > error: test failed, to rerun pass `--bin shadowenv`
       For full logs, run 'nix log /nix/store/a340k0chdxzmlaf996rr1mldb128ibqk-shadowenv-3.0.3.drv'.

Start by running nix-build -A shadowenv and inspect src/loader.rs:104, where the reported unwrap failures occur. Focus on the four failing loader::tests::find_shadowenv_paths_* tests and determine why they intermittently encounter a missing path. Done means the tests pass reliably and the Nix build succeeds on the first try.