build(deps-dev): bump web-ext from 5.5.0 to 6.0.0 in /addon

Bumps [web-ext](https://github.com/mozilla/web-ext) from 5.5.0 to 6.0.0.
- [Release notes](https://github.com/mozilla/web-ext/releases)
- [Commits](mozilla/web-ext@5.5.0...6.0.0)

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