iOS testbed runner incompatible with GitHub Actions `macos-15` runner.

[freakboy3742]

Bug report

Bug description:

Microsoft's 20250811 macos-15 image update made some significant changes that are incompatible with CPython's iOS test runner.

This prevents the Cpython iOS testbed runner from operating on macos-15 machines in GitHub Actions, and in Azure Pipelines.

At this time, Microsoft's advice is to use the macos-14 image instead.

The Xcode project itself is able to run on the macos-15 image; however, something about the log streaming technique used by the testbed runner breaks the process of Xcode launching the simulator to run the test suite.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Other

Linked PRs

• gh-137973: Add a non-parallel test plan to the iOS testbed project #138018
• [3.14] gh-137973: Add a non-parallel test plan to the iOS testbed project (GH-138018) #138038
• [3.13] gh-137973: Add a non-parallel test plan to the iOS testbed project (GH-138018) #138039