Upgrade Eslint to version 9

[w3nl]

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Comments skipped due to low confidence (2)

src/tests/enum.test.js:64

• The error message should end with a period for consistency: 'Invalid Encoding key UTF-8.'

assert.strictEqual(error.message, 'Invalid Encoding key UTF-8')

src/tests/enum.test.js:72

• The error message should end with a period for consistency: 'Invalid Encoding value utf-8.'

assert.strictEqual(error.message, 'Invalid Encoding value utf-8')