Allow fallback to a different version of Xcode in integration tests.
Allow fallback to a different version of Xcode in integration tests.

This allows us to fix a default version for CI, but still support local test runs with different versions without updating the script runner.

RELNOTES: None.
PiperOrigin-RevId: 159595762

bazelbuild/rules_apple,bazelbuild/rules_apple,bazelbuild/rules_apple,bazelbuild/rules_apple