build(deps-dev): bump web-ext from 6.0.0 to 6.1.0 in /addon (#908)

Bumps [web-ext](https://github.com/mozilla/web-ext) from 6.0.0 to 6.1.0.
- [Release notes](https://github.com/mozilla/web-ext/releases)
- [Commits](mozilla/web-ext@6.0.0...6.1.0)

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Author: dependabot[bot]