Update to Pester 4.8.0

[SteveL-MSFT]

PR Summary

This version of Pester contains a fix so that $TestDrive on Windows uses the long path and not the 8.1 short path which causes many failures in our netcore30 working branch. After this works on master, I'll take it into feature-netcore30 branch and remove the workarounds.

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[iSazonov]

Should we revert our workarounds for long paths?

[SteveL-MSFT]

@iSazonov yes, I'll do that in the feature-netcore30 branch after picking up this commit