test: Python 3.10+ union-style param in function tool

[RezaRahemtola]

What does this PR do?

Adds a test for the chat template generation issue fixed here: huggingface/transformers#35103

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or Telegram? Please add a link
  to it if that's the case.
• Did you write any new necessary tests?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.69%. Comparing base (b4bf68a) to head (e3c8359).
Report is 2 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #22   +/-   ##
=======================================
  Coverage   84.69%   84.69%           
=======================================
  Files          12       12           
  Lines         281      281           
=======================================
  Hits          238      238           
  Misses         43       43           

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