ci: :arrow-up: bump vscode-extension-tester from 8.17.0 to 8.18.0

Bumps [vscode-extension-tester](https://github.com/redhat-developer/vscode-extension-tester/tree/HEAD/packages/extester) from 8.17.0 to 8.18.0.
- [Release notes](https://github.com/redhat-developer/vscode-extension-tester/releases)
- [Commits](https://github.com/redhat-developer/vscode-extension-tester/commits/v8.18.0/packages/extester)

---
updated-dependencies:
- dependency-name: vscode-extension-tester
  dependency-version: 8.18.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]