Test failures in `@actions/exec` package when run under MacOS

Sometime between 2024-10-08 and 2024-10-28 there are three unit tests from the @actions/exec package which have started failing when run specifically on MacOS.

• Last successful run
• First failing run

The failures do not appear to be related to any code changes in the repo (I can repro the issue with exactly the same code which was running successfully on October 8th). My guess is that the failures may have something to do with the runner image. The last passing test was running under macos-14-arm64@20240922.1 while the failures are occurring under macos-14-arm64@20241007.259.

The three failing tests are the following:

• @actions/exec › Handles child process holding streams open
• @actions/exec › Handles child process holding streams open and non-zero exit code
• @actions/exec › Handles child process holding streams open and stderr

One interesting data point . . . these same tests will PASS when run in GitHub Actions if I change the runner type from macos-latest to macos-latest-large:

• Successful run under macos-latest-large

Start with packages/exec/tests/exec.test.ts at the three named tests around lines 360, 406, and 460, then compare the linked passing and failing GitHub Actions runs and macOS runner images. Reproduce the failures on macos-14-arm64 and compare with macos-latest-large. Done means the cause is identified and the three tests pass reliably on the affected runner configuration.