chore(deps-dev): bump vscode-extension-tester from 5.1.0 to 5.2.1

Bumps [vscode-extension-tester](https://github.com/redhat-developer/vscode-extension-tester) from 5.1.0 to 5.2.1.
- [Release notes](https://github.com/redhat-developer/vscode-extension-tester/releases)
- [Changelog](https://github.com/redhat-developer/vscode-extension-tester/blob/master/CHANGELOG.md)
- [Commits](redhat-developer/vscode-extension-tester@v5.1.0...v5.2.1)

---
updated-dependencies:
- dependency-name: vscode-extension-tester
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]