Implement PartialEq for ProtocolError

Summary:
Needed for unit testing expected errors in an upcoming diff:

https://www.internalfb.com/code/fbsource/[3ebe96df25f7dfc9df57b4d26e6357842b993db4]/fbcode/thrift/lib/rust/src/tests/binary.rs?lines=526-530

Reviewed By: zertosh

Differential Revision: D68986438

fbshipit-source-id: c7b540fe9672023001348336217dc0b65e270cbb

third-party/thrift/src/thrift/lib/rust/src/errors.rs

@@ -20,7 +20,7 @@ use thiserror::Error;
 use crate::ttype::TType;
 use crate::ApplicationException;
 
-#[derive(Debug, Error)]
+#[derive(Debug, Error, PartialEq)]
 #[allow(dead_code)]
 pub enum ProtocolError {
     #[error("end of file reached")]