build(deps-dev): Bump web-ext from 3.2.1 to 4.0.0 in /addon (#350)

Bumps [web-ext](https://github.com/mozilla/web-ext) from 3.2.1 to 4.0.0.
- [Release notes](https://github.com/mozilla/web-ext/releases)
- [Commits](mozilla/web-ext@3.2.1...4.0.0)

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

Author: dependabot-preview[bot]