Fix test_pep352 and test_attrinjector regressions

Add CancelledError to exception_hierarchy.txt so test_pep352
test_inheritance accounts for the new builtin exception.

Isolate test_async in a separate process to prevent it from
loading IronPythonTest assembly which causes duplicate
SpecialName GetBoundMember on XmlElement in test_attrinjector.

Author: mikasoukhov

src/core/IronPython.StdLib/lib/test/exception_hierarchy.txt

@@ -5,6 +5,7 @@ BaseException
  +-- Exception
       +-- StopIteration
       +-- StopAsyncIteration
+      +-- CancelledError
       +-- ArithmeticError
       |    +-- FloatingPointError
       |    +-- OverflowError

tests/IronPython.Tests/Cases/IronPythonCasesManifest.ini

@@ -4,6 +4,9 @@ WorkingDirectory=$(TEST_FILE_DIR)
 Redirect=false
 Timeout=120000 # 2 minute timeout
 
+[IronPython.test_async]
+IsolationLevel=PROCESS # loads IronPythonTest assembly, causes a failure in IronPython.test_attrinjector
+
 [IronPython.test_builtin_stdlib]
 RunCondition=NOT $(IS_MONO)
 Reason=Exception on adding DocTestSuite