Bump pdfjs-dist from 5.4.624 to 5.5.207 in /ui-tests

Bumps [pdfjs-dist](https://github.com/mozilla/pdf.js) from 5.4.624 to 5.5.207.
- [Release notes](https://github.com/mozilla/pdf.js/releases)
- [Commits](mozilla/pdf.js@v5.4.624...v5.5.207)

---
updated-dependencies:
- dependency-name: pdfjs-dist
  dependency-version: 5.5.207
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]