Reduce test-python-environment.yml to run on certain conditions

[ArBridgeman]

closes #731

Checklist

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For any Pull Request

Is the following correct:

• the title of the Pull Request?
• the title of the corresponding issue?
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• that the issue which this Pull Request fixes ("Fixes...") is mentioned?

When Changes Were Made

Did you:

• update the changelog?
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[ArBridgeman]

• ✅ Test that does not run the tests anymore without changes
  https://github.com/exasol/python-toolbox/actions/runs/24510967854
• ✅ Test that runs when there are changes & if they fail it blocks the PR

https://github.com/exasol/python-toolbox/actions/runs/24511438053 * will not test main until it's been merged

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud