build(deps-dev): bump web-ext from 6.3.0 to 6.6.0 in /addon

Bumps [web-ext](https://github.com/mozilla/web-ext) from 6.3.0 to 6.6.0.
- [Release notes](https://github.com/mozilla/web-ext/releases)
- [Commits](mozilla/web-ext@6.3.0...6.6.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]