Update to use the forward-looking proper noun "ProtoJSON" for the canonical JSON encoding.

PiperOrigin-RevId: 823554361

Author: protobuf-github-bot

src/google/protobuf/timestamp.proto

@@ -112,8 +112,8 @@ option csharp_namespace = "Google.Protobuf.WellKnownTypes";
 // {hour}, {min}, and {sec} are zero-padded to two digits each. The fractional
 // seconds, which can go up to 9 digits (i.e. up to 1 nanosecond resolution),
 // are optional. The "Z" suffix indicates the timezone ("UTC"); the timezone
-// is required. A proto3 JSON serializer should always use UTC (as indicated by
-// "Z") when printing the Timestamp type and a proto3 JSON parser should be
+// is required. A ProtoJSON serializer should always use UTC (as indicated by
+// "Z") when printing the Timestamp type and a ProtoJSON parser should be
 // able to accept both UTC and other timezones (as indicated by an offset).
 //
 // For example, "2017-01-15T01:30:15.01Z" encodes 15.01 seconds past