Don't re-use XmlSchemaSet - it's not threadsafe.#74524

StephenMolloy merged 1 commit intodotnet:maindotnet/runtime:mainfrom

StephenMolloy:74370_Making-DCS-Import-Tests-More-RobustStephenMolloy/runtime:74370_Making-DCS-Import-Tests-More-RobustCopy head branch name to clipboard