unified_exec::tests::unified_exec_timeouts fails when run locally

[ahornby]

unified_exec::tests::unified_exec_timeout is matching on "codex" which is causing false positives when running tests locally, presumably the string shows up elsewhere in the output coincidentally.

Reproduces for me on fedora 43 x86_64 on main 764f3c7 with:

cargo nextest run --all-features --no-fail-fast unified_exec::tests::unified_exec_timeouts
    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.38s
────────────
 Nextest run ID fa2b4949-a66c-408c-8002-32c52c70ec4f with nextest profile: default
    Starting 1 test across 107 binaries (3211 tests skipped)
        FAIL [   5.667s] codex-core unified_exec::tests::unified_exec_timeouts
  stdout ───

    running 1 test
    test unified_exec::tests::unified_exec_timeouts ... FAILED

    failures:

    failures:
        unified_exec::tests::unified_exec_timeouts

    test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 774 filtered out; finished in 5.66s
    
  stderr ───

    thread 'unified_exec::tests::unified_exec_timeouts' (459601) panicked at core/src/unified_exec/mod.rs:381:9:
    timeout too short should yield incomplete output
    note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

────────────
     Summary [   5.677s] 1 test run: 0 passed, 1 failed, 3211 skipped
        FAIL [   5.667s] codex-core unified_exec::tests::unified_exec_timeouts
error: test run failed