Skip Xcode 16.0 and 16.1 in PR workflow

[natecook1000]

These two Xcode versions are no longer installed in the runner image.

Checklist

• I've read the Contribution Guidelines
• My contributions are licensed under the Swift license.
• I've followed the coding style of the rest of the project.
• I've added tests covering all new code paths my change adds to the project (if appropriate).
• I've added benchmarks covering new functionality (if appropriate).
• I've verified that my change does not break any existing tests or introduce unexplained benchmark regressions.
• I've updated the documentation if necessary.

[natecook1000]

@swift-ci Please test

[lorentey]

🙇‍♂️