Pin yarn version

[Strift]

Pull Request

What does this PR do?

• Pin yarn version in package.json to use use v4.x
• Regenerate yarn.lock
• Update Github action code to use v4.x
• Add missing eslint devDependency (was probably included in the old yarn.lock)
• Fix cypress linting errors

PR checklist

Please check if your PR fulfills the following requirements:

• Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
• Have you read the contributing guidelines?
• Have you made sure that the title is accurate and descriptive of the changes?

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