Sync Kotlin protobuf version with Java protobuf version

[LarsSven]

Quarkus 3.21 added support for the Kotlin extension of Java gRPC. With this support however, protobuf-kotlin was given a protobuf V4 version. The Java protobuf version published by Quarkus is however a protobuf V3 version. V4 has a breaking change around a class rename of GeneratedMessageV3 to GeneratedMessage, which is one of the reasons Quarkus is still on V3.

Publishing a V4 version of Kotlin but a V3 version of Java causes incompatibility exactly due to this breaking change. So the project I work on which is using Quarkus is getting the following error:

Reason:
  Type 'com/google/protobuf/GeneratedMessageV3$FieldAccessorTable' (current frame, stack[0]) is not assignable to 'com/google/protobuf/GeneratedMessage$FieldAccessorTable' (from method signature)

This is fixed by giving protobuf-kotlin a V3 version. I think it makes sense for both Java and Kotlin to always be synced up, so I simply change the hardcoded protobuf-kotlin version to the protoc version that Java is using too, which changes Kotlin to a V3 version.

Note that theoretically, the versions of different languages of protobuf may diverge. While the minor and patch version will always be the same, the major version may change if one language has a breaking change but another does not. So theoretically Kotlin may at some point get a version like 6.80.1 while Java would be 7.80.1, however, I would say this is unlikely since Kotlin extends the Java implementation, whereas something like C# and Java diverting I would say would be an actual possibility.

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[LarsSven]

Thanks for your pull request!

Your pull request does not follow our editorial rules. Could you have a look?

• title should preferably start with an uppercase character (if it makes sense!)

Had a space in front of the title accidentally, I removed the space

[gsmet]

Thanks! This seems to makes sense to me but we probably need to document it in the migration guide.

Asked a proper review to @alesj and @cescoffier .