Disable failing ctypes tests

Author: BCSharp

tests/IronPython.Tests/Cases/CPythonCasesManifest.ini

@@ -17,6 +17,14 @@ Reason=Current implementation of get_last_error needs to be debugged
 [CPython.ctypes.test_functions]
 Ignore=true
 
+[CPython.ctypes.test_frombuffer]
+RunCondition=NOT $(IS_MONO)
+Reason=Depends on gc.collect() calling finalizers
+
+[CPython.ctypes.test_macholib]
+Ignore=true
+Reason=TODO: OSX specific: ctypes.macholib.dyld is outdated and does not perform OK on modern macOS
+
 [CPython.ctypes.test_objects]
 Ignore=true
 Reason=CPython implementation detail