Bump externals/sgdk from cb114ac to 6a88e15 (#707)

Bumps [externals/sgdk](https://github.com/Stephane-D/SGDK) from `cb114ac` to `6a88e15`.
- [Release notes](https://github.com/Stephane-D/SGDK/releases)
- [Commits](Stephane-D/SGDK@cb114ac...6a88e15)

---
updated-dependencies:
- dependency-name: externals/sgdk
  dependency-version: 6a88e15d121c6f0aeaad58caf30e8412c461a9fc
  dependency-type: direct:production
...

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