[Commands] Migrate: Don't attempt to cache manifest with temporary feature flags

The build system requested by the `swift package migrate` command is
transitory and shouldn't be persisted. This would also make sure that
the build plan is always available regardless of what builds happened
before `swift package migrate` invocation.

Resolves: rdar://152687084

Author: xedin

Sources/Commands/PackageCommands/Migrate.swift

@@ -206,6 +206,9 @@ extension SwiftPackageCommand {
 
             return try await swiftCommandState.createBuildSystem(
                 traitConfiguration: .init(),
+                // Don't attempt to cache manifests with temporary
+                // feature flags added just for migration purposes.
+                cacheBuildManifest: false,
                 productsBuildParameters: destinationBuildParameters,
                 toolsBuildParameters: toolsBuildParameters,
                 // command result output goes on stdout