Correct package XCode version to 12.4
Correct package XCode version to 12.4

The prior version was no longer on the system and the system default
was used.

blowekamp/SimpleITK,blowekamp/SimpleITK,InsightSoftwareConsortium/SimpleITK,InsightSoftwareConsortium/SimpleITK,SimpleITK/SimpleITK,blowekamp/SimpleITK,blowekamp/SimpleITK,SimpleITK/SimpleITK,blowekamp/SimpleITK,SimpleITK/SimpleITK,blowekamp/SimpleITK,blowekamp/SimpleITK,SimpleITK/SimpleITK,SimpleITK/SimpleITK,SimpleITK/SimpleITK,InsightSoftwareConsortium/SimpleITK,InsightSoftwareConsortium/SimpleITK,InsightSoftwareConsortium/SimpleITK,InsightSoftwareConsortium/SimpleITK,SimpleITK/SimpleITK,InsightSoftwareConsortium/SimpleITK,SimpleITK/SimpleITK,blowekamp/SimpleITK,InsightSoftwareConsortium/SimpleITK