chore(deps-dev): bump @existdb/gulp-exist from 5.0.0 to 6.0.0

Bumps [@existdb/gulp-exist](https://github.com/eXist-db/gulp-exist) from 5.0.0 to 6.0.0.
- [Release notes](https://github.com/eXist-db/gulp-exist/releases)
- [Commits](eXist-db/gulp-exist@v5.0.0...v6.0.0)

---
updated-dependencies:
- dependency-name: "@existdb/gulp-exist"
  dependency-version: 6.0.0
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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Author: dependabot[bot]