PR Summary

Increase maximum number over time until we find a stable upper limit. It turns out one cannot do a straightforward calculation of runspaces (either due to complexity or garbage collection)
An example build failure with 14 runspaces is here: https://ci.appveyor.com/project/PowerShell/psscriptanalyzer/builds/28399656/job/8d7spi13o6kekjaw?fullLog=true

cc Thomas Rayner (@thomasrayner) for visiblity

PR Checklist

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