Collect the number of cpu cores using psutil.cpu_count()

[steveny91]

What does this PR do?

Small change in logic in how we collect number of cpu cores. We used to count the length of CPU times, but there's a built in function in psutil that returns the count.

Was initially part of #13349 but it was better to split them up.

[github-actions]

Label changelog/Changed was added to this Pull Request, so the next release will bump major version. Please make sure this is a breaking change, or use the changelog/Fixed label.

[github-actions]

Label changelog/Changed was added to this Pull Request, so the next release will bump major version. Please make sure this is a breaking change, or use the changelog/Fixed label.

[codecov]

Codecov Report

Merging #13483 (e707143) into master (d087f87) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Flag	Coverage Δ
system_core	90.90% <100.00%> (+0.28%)	⬆️

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