chore: Update to eslint 9

[marikaner]

While integrating dependabot PRs, I noticed, that we are weirdly using two versions of eslint (8 + 9). I don't see a reason why this was done and I assume, that this was by mistake. Let me know, if I missed something.

[ZhongpinWang]

LGTM

[ZhongpinWang]

Only one comment, do we need a changeset for this? As using ESLint9 potentially needs consumers to adapt some of their eslint rules (just like in this PR some eslint disable was removed/added).

[KavithaSiva]

Like @ZhongpinWang said I think, adding a changeset with compatbility note is good, as eslint config from 8 to 9 is breaking, with the flat config structure.

[marikaner]

Only one comment, do we need a changeset for this? As using ESLint9 potentially needs consumers to adapt some of their eslint rules (just like in this PR some eslint disable was removed/added).

Yes, I will add a changeset for the peer dependency update. With that users should be able to use eslint 9 without the --legacy-peer-deps flag.
Otherwise, I only changed dev dependencies and I did not change any lint rules. We now use eslint 9 consistently throughout the code, but that does not affect users.