Bump engine.io and socket.io in /gatsby (#1451)

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

Updates `engine.io` from 3.5.0 to 3.6.0
- [Release notes](/~https://github.com/socketio/engine.io/releases)
- [Changelog](/~https://github.com/socketio/engine.io/blob/main/CHANGELOG.md)
- [Commits](socketio/engine.io@3.5.0...3.6.0)

Updates `socket.io` from 2.4.1 to 2.5.0
- [Release notes](/~https://github.com/socketio/socket.io/releases)
- [Changelog](/~https://github.com/socketio/socket.io/blob/2.5.0/CHANGELOG.md)
- [Commits](socketio/socket.io@2.4.1...2.5.0)

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

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Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>