ci: self-lint eslint config style

[MikeMcC399]

Issue

For styling consistency with the rest of the repo, eslint.config.mjs should not be linted by Prettier.

Change

• Add eslint.config.mjs to .prettierignore

• Add eslint.config.mjs with @stylistic/eslint-plugin to itself

• Use npx eslint eslint.config.mjs --fix to fix trailing commas

Verification

Execute the following and confirm that no errors are reported or changes suggested:

git clean -xfd
npm ci
npx eslint
npx prettier eslint.config.mjs --check # should be ignored

[cypress-app-bot]

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[github-actions]

🎉 This PR is included in version 6.7.16 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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