Fix type error for path usage

[eaidova]

What does this PR do?

fixing bug found during internal validation:

  File "/opt/hostedtoolcache/Python/3.10.15/x64/lib/python3.10/site-packages/optimum/exporters/openvino/__main__.py", line 341, in main_export
    dtype = deduce_diffusers_dtype(
  File "/opt/hostedtoolcache/Python/3.10.15/x64/lib/python3.10/site-packages/optimum/exporters/openvino/utils.py", line 246, in deduce_diffusers_dtype
    if (path / "transformer").is_dir():
TypeError: unsupported operand type(s) for /: 'str' and 'str'

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

[HuggingFaceDocBuilderDev]

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