Bump engine.io and gatsby (#381)

Bumps [engine.io](https://github.com/socketio/engine.io) and [gatsby](https://github.com/gatsbyjs/gatsby). These dependencies needed to be updated together.

Updates `engine.io` from 4.1.2 to 6.2.1
- [Release notes](https://github.com/socketio/engine.io/releases)
- [Changelog](https://github.com/socketio/engine.io/blob/main/CHANGELOG.md)
- [Commits](https://github.com/socketio/engine.io/compare/4.1.2...6.2.1)

Updates `gatsby` from 5.0.0 to 5.4.1
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/compare/gatsby@5.0.0...gatsby@5.4.1)

---
updated-dependencies:
- dependency-name: engine.io
  dependency-type: indirect
- dependency-name: gatsby
  dependency-type: indirect
...

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