Explicitly set python version in GitHub workflow for testing with oneMath

[antonwolfy]

The PR updates conda-incubator/setup-miniconda step in the GH workflow for testing with oneMath to explicitly set python version the same as defined in testing matrix, otherwise the latest available python will be taken.

• Have you provided a meaningful PR description?
• Have you added a test, reproducer or referred to an issue with a reproducer?
• Have you tested your changes locally for CPU and GPU devices?
• Have you made sure that new changes do not introduce compiler warnings?
• Have you checked performance impact of proposed changes?
• Have you added documentation for your changes, if necessary?
• Have you added your changes to the changelog?

[github-actions]

Array API standard conformance tests for dpnp=0.20.0dev0=py313h509198e_22 ran successfully.
Passed: 1227
Failed: 0
Skipped: 9

[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/index.html

[coveralls]

coverage: 83.312%. remained the same
when pulling 1f348fc on add-missing-python-version-to-onemath-gh-workflow
into 96e12cf on master.

[antonwolfy]

The workflow is passing now:
https://github.com/IntelPython/dpnp/actions/runs/18905585891

[vlad-perevezentsev]

LGTM
Thank you @antonwolfy