[refurb] Fix false positive on empty tuples (FURB168)

[MeGaGiGaGon]

Summary

This PR fixes #19047 / the isinstance-type-none (FURB168) tuple false positive by adding a check if the tuple is empty to the code. I also noticed there was another false positive with the other tuple check in the same function, so I fixed it the same way. Union[()] is invalid at runtime with TypeError: Cannot take a Union of no types., but it is accepted by basedpyright playground and is equivalent to Never, so I fixed it anyways. I'm getting on a side tangent here, but it looks like MyPy doesn't accept it, and ty playground gives @Todo.

Test Plan

Added two test cases for the two false positives. playground

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

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[ntBre]

Thanks!