Bump @blockly/theme-dark from 7.0.12 to 8.0.3 in /src-editor

Bumps [@blockly/theme-dark](https://github.com/RaspberryPiFoundation/blockly-samples/tree/HEAD/plugins/theme-dark) from 7.0.12 to 8.0.3.
- [Release notes](https://github.com/RaspberryPiFoundation/blockly-samples/releases)
- [Changelog](https://github.com/RaspberryPiFoundation/blockly-samples/blob/main/plugins/theme-dark/CHANGELOG.md)
- [Commits](https://github.com/RaspberryPiFoundation/blockly-samples/commits/@blockly/theme-dark@8.0.3/plugins/theme-dark)

---
updated-dependencies:
- dependency-name: "@blockly/theme-dark"
  dependency-version: 8.0.3
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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Author: dependabot[bot]