Use IsolationLevel=PROCESS

Author: slozier

Src/IronPythonTest/Cases/IronPythonCasesManifest.ini

@@ -54,6 +54,9 @@ Ignore=true
 Ignore=true
 Reason=Requires powershell
 
+[IronPython.test_io_stdlib]
+IsolationLevel=PROCESS # https://github.com/IronLanguages/ironpython3/issues/1808
+
 [IronPython.test_ipyc]
 Ignore=true
 Reason=New test needs to be written for new csharp version