Add retry to test_byteswap

Author: slide

Src/IronPythonTest/Cases/CTypesCPythonCasesManifest.ini

@@ -6,6 +6,9 @@ Redirect=false
 RunCondition=NOT $(IS_NETCOREAPP) AND NOT $(IS_MACOS)
 Reason=ctypes is not working on .NET Core yet
 
+[CTypesCPython.test_byteswap]
+RetryCount=2
+
 [CTypesCPython.test_errno]
 Ignore=true
 Reason=Current implementation of get_last_error needs to be debugged