Decorator to make sure we can import `core` from caffe2 (#19273)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19273
Some of the CIs are failing if the protobuf is not installed. Protobuf is imported as part of the `caffe2.python.core`, and this adds a skip decorator to avoid running tests that depend on `caffe2.python.core`
Reviewed By: jianyuh
Differential Revision: D14936387
fbshipit-source-id: e508a1858727bbd52c951d3018e2328e14f126be
