Use protobuf version 3 (#2558)
Use protobuf version 3 (#2558)

Protobuf introduced major version 4.21.0, which contains breaking changes

This is a quick fix which pins protobuf to 3.20.1 before we eventually migrate the codebase to proto4

Co-authored-by: kokrui <92e67b68d6d247a459efd22912b1ad0d54e6bfee@gmail.com>
trailofbits/manticore,trailofbits/manticore,trailofbits/manticore