update setup-python action version

[breedenc]

Description

Updates the version of the setup-python GitHub Action used for backend and orchestrator unit tests.

Motivation and Context

Currently-used version is several major versions behind. This updates to latest.

How Has This Been Tested?

Tested by triggering the backend and orchestrator unit test workflows with the new dependency version.

• backend workflow test
• orchestrator workflow test

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation change
• Unit test workflow update only

Checklist

• My code follows conforms to the coding standards.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

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