Remove duplicated key in dict. NFC. (#15608)

Author: kleisauke

tests/test_posixtest.py

@@ -70,7 +70,6 @@ def get_pthread_tests():
 unsupported = {
   'test_pthread_attr_setinheritsched_2_2': 'scheduling policy/parameters are not supported',
   'test_pthread_attr_setinheritsched_2_3': 'scheduling policy/parameters are not supported',
-  'test_pthread_attr_setinheritsched_2_3': 'scheduling policy/parameters are not supported',
   'test_pthread_attr_setinheritsched_2_4': 'scheduling policy/parameters are not supported',
   'test_pthread_attr_setschedparam_1_3': 'scheduling policy/parameters are not supported',
   'test_pthread_attr_setschedparam_1_4': 'scheduling policy/parameters are not supported',