avro

AVRO-3055: Bump protobuf-java from 3.14.0 to 3.15.1 in /lang/java (#1099)

Bumps [protobuf-java](https://github.com/protocolbuffers/protobuf) from 3.14.0 to 3.15.1.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/master/generate_changelog.py)
- [Commits](https://github.com/protocolbuffers/protobuf/compare/v3.14.0...v3.15.1)

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