Change back to use powershell.exe in 'SetVersionVariables.yml' to unblock daily build

[daxian-dbw]

PR Summary

PR #11126 changed - powershell: to - pwsh: to get consistent JSON conversion for DateTime.
However, it turns out our current build agents don't have pwsh installed and it causes the daily build to fail.
Revert the change for now, and will redo when the pwsh installation issue is resolved for our build agents.

PR Context

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[ghost]

🎉v7.1.0-preview.1 has been released which incorporates this pull request.:tada:

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