enable tests in getdeps
enable tests in getdeps

Summary: also always install fizz test headers for mvfst and proxygen tests to consume without needing to build fizz tests

Reviewed By: yfeldblum

Differential Revision: D23676344

fbshipit-source-id: 7ae78c81c2d67bb8da135fcd69d4be119b50a27e

facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst