Upgraded eslint-plugin to 20.0.0

Purpose

The MR upgrades the @gitlab/eslint-plugin to 20.0.0. It's not coming from the renovate bot because the relevant MR failed, and this MR addresses the failed job in the renovate bot's MR.

Screenshots

Checklist

For a new icon and/or illustration:

• Link to related design issue:
• If this adds an icon ensure that it follows the new icon checklists.
• If this adds an illustration ensure that it follows the new illustration checklists.

For third-party trademarks:

• If this adds or updates an icon or illustration that includes a third-party trademark, ensure that it follows the process for adding third-party trademarks to GitLab.