[Tests] use re-exported `RuleTester`

[G-Rath]

This switches all tests over to sourcing RuleTester from an internal location which currently re-exports RuleTester from eslint, making it easier to later replace with a custom implementation to support ESLint v9 flat config

Also see #2996

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 90.53%. Comparing base (743ebca) to head (5e36aa6).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3071 +/- ## ========================================== - Coverage 95.13% 90.53% -4.61% ========================================== Files 82 82 Lines 3559 3559 Branches 1243 1243 ========================================== - Hits 3386 3222 -164 - Misses 173 337 +164 ``` | [Flag](https://app.codecov.io/gh/import-js/eslint-plugin-import/pull/3071/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=import-js) | Coverage Δ | | |---|---|---| | [](https://app.codecov.io/gh/import-js/eslint-plugin-import/pull/3071/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=import-js) | `90.53% <ø> (-4.61%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=import-js#carryforward-flags-in-the-pull-request-comment) to find out more.

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