[JIT] Improve error message when type annotation Future without a contained type (#39751)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/39751
Test Plan: Imported from OSS
Reviewed By: eellison
Differential Revision: D21960368
Pulled By: jamesr66a
fbshipit-source-id: 8650d31ff8070b12672c8d4b0224d4e69f619938
