Update typescript-eslint packages to v6.x

We can safely update to v6.x of typescript-eslint packages. The main breaking changes are Node v18, which we use: https://github.com/typescript-eslint/typescript-eslint/blob/main/CHANGELOG.md#600-2023-07-10 .

This is necessary to fix [this error]( ), which is holding back newer TS versions.

We can not yet update to v7.x as it requires ESLint 8.56.0+, and updating ESLint to v8+ is outside the scope of this change.