Reduce log output when no tests are prioritized (#101803)
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### <samp>🤖 Generated by Copilot at 733b991</samp>
Improve test reordering output in `tools/testing/test_selections.py`. Add a check to only print reordering information when there are tests to prioritize.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/101803
Approved by: https://github.com/malfet, https://github.com/kit1980
