add flag to xcodebuild to skip package plugin validation

[NikolaiMadlener]

Skip Package Plugin Validation

:recycle: Current situation & Problem

Xcode projects relying on package plugins do not run successfully with our Xcode build workflow. To resolve this issue an additional build argument should be added to skip the plugin validation.

:gear: Release Notes

• add build argument skipPackagePluginValidation to Xcode build command in the Xcode build workflow

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