Update dependency eslint-config-amo to v3.9.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
eslint-config-amo	devDependencies	minor	3.8.0 -> 3.9.0

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Release Notes

mozilla/eslint-config-amo

### [`v3.9.0`](https://togithub.com/mozilla/eslint-config-amo/releases/3.9.0) [Compare Source](https://togithub.com/mozilla/eslint-config-amo/compare/3.8.0...3.9.0) - Lock file maintenance since `3.8.0`

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