[clang-format] Fix an ObjC regression introduced with new...

[clang-format] Fix an ObjC regression introduced with new [[likely]][[unlikely]] support in if/else clauses

Summary:
{D80144} introduce an ObjC regression

Only parse the `[]` if what follows is really an attribute

Reviewers: krasimir, JakeMerdichAMD

Reviewed By: krasimir

Subscribers: rdwampler, aaron.ballman, curdeius, cfe-commits

Tags: #clang, #clang-format

Differential Revision: https://reviews.llvm.org/D80547