Fix broken ESLint by pinning to `2.2.20-Insiders` release (#9215)

This fixes #9213 by pinning ESLint to `2.2.20-Insiders` which is the
last known version to work well with Zed.

Once this fix is out, we can take a closer look at upgrading to 2.4.x or
even 3.x once that's out of prerelease.

Release Notes:

- Fixed ESLint integration being broken after Mar 7 2024 due to ESLint
3.0.1 alpha release being pushed.
([#9213](https://github.com/zed-industries/zed/issues/9213)).