Protobuf rebuilt for version 4.21

What's Changed

• Bump-protobuf-max-version by @james-shull-at-oura in #12
• Version 6.6.0 by @james-shull-at-oura in #13

New Contributors

• @james-shull-at-oura made their first contribution in #12

Full Changelog: v6.5.0...v6.6.0