chore: lock linting and formatting dev dependencies

[mcous]

Avoids uncontrolled formatting / lint drift in the absence of a developer lockfile. Personally, I would prefer a lockfile, but that seems like a larger discussion/change. See https://github.com/testing-library/svelte-testing-library/pull/301#issuecomment-1915570446 for locking rationale.

I tried to lock the versions at the latest semver compatible release of each library

[github-actions[bot]]

:tada: This PR is included in version 4.2.0 :tada:

The release is available on:

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

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