Test target `parallelizable` behaviour changed in 2.44.0

[CraigSiemens]

After updating from 2.43.0 to 2.44.0 we noticed our tests behaving differently (and failing). We narrowed it down to the scheme being generated differently when parallelizable: true is set on the test target.

Expected Behaviour

The test target parallelization used to be "Enabled"

Actual Behaviour

The test target parallelization is now "Swift Testing only"

[CraigSiemens]

After some more digging, it appears to be caused by updating Xcodeproj to 8.27.7.

Xcodeproj added a new parallelization option and deprecated parallelizable. It appears their mapping from deprecated option to the new option causes "true" to map to .swiftTestingOnly, which is different than how it previously behaved.

https://github.com/tuist/XcodeProj/blob/8.27.7/Sources/XcodeProj/Scheme/XCScheme%2BTestableReference.swift#L9-L13

It's possible this could be worked around in Xcodegen by doing it's own mapping from parallelizable to parallelization so that true mapped to .enabled.