build(deps-dev): bump web-ext from 8.6.0 to 8.7.1 in /addon (#2662)

Bumps [web-ext](https://github.com/mozilla/web-ext) from 8.6.0 to 8.7.1.
- [Release notes](https://github.com/mozilla/web-ext/releases)
- [Commits](mozilla/web-ext@8.6.0...8.7.1)

---
updated-dependencies:
- dependency-name: web-ext
  dependency-version: 8.7.1
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]