eslint 9 support for `eslint-plugin-prefer-let`

[deanmarano]

Hi there! We're enjoying the prefer-let eslint rule you have published in our app. We're migrating to the latest version of eslint, which uses a different configuration for rule definitions. I'd like to update your plugin. It does require some pretty significant changes (basically touching every file, another plugin I've updated as example), and I wanted to check and make sure you'd be open to it.

[cowboyd]

@deanmarano Absolutely we would be open for it!