Bump jelix/jelix from 1.8.18.1 to 1.8.21

Bumps [jelix/jelix](https://github.com/jelix/jelix) from 1.8.18.1 to 1.8.21.
- [Release notes](https://github.com/jelix/jelix/releases)
- [Changelog](https://github.com/jelix/jelix/blob/v1.8.21/CHANGELOG-1.8.md)
- [Commits](jelix/jelix@v1.8.18.1...v1.8.21)

---
updated-dependencies:
- dependency-name: jelix/jelix
  dependency-version: 1.8.21
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]