SI-8497 Fix regression in pickling of AnnotatedTypes

Fixes an inconsistency introduced in these two spots:

  https://github.com/scala/scala/pull/3033/files#diff-6ce1a17ebee31068f41c36a8a2b3bc9aR79
  https://github.com/scala/scala/pull/3033/files#diff-c455cb229f5227b1bcaa1544478fe3acR452

The bug shows up when pickling then unpickling an AnnotatedType
that has only non-static annotations.
Merge pull request #3682 from retronym/ticket/8497

SI-8497 Fix regression in pickling of AnnotatedTypes