Update import for PackageModel

With upcoming changes to SwiftPM's TraitConfiguration
(see #8370), PackageModel needs to be imported using
`@preconcurrency`.

Author: bripeticca

Sources/BuildSystemIntegration/SwiftPMBuildSystem.swift

@@ -20,7 +20,7 @@ package import LanguageServerProtocol
 import LanguageServerProtocolExtensions
 @preconcurrency import PackageGraph
 import PackageLoading
-import PackageModel
+@preconcurrency import PackageModel
 import SKLogging
 package import SKOptions
 @preconcurrency package import SPMBuildCore