bpo-40147: Move the check for duplicate keywords to the compiler (GH-19289)

diff --git a/Lib/test/test_metaclass.py b/Lib/test/test_metaclass.py
index e6fe20a..6edd899 100644
--- a/Lib/test/test_metaclass.py
+++ b/Lib/test/test_metaclass.py
@@ -128,7 +128,7 @@
     ...
     Traceback (most recent call last):
     [...]
-    SyntaxError: keyword argument repeated
+    SyntaxError: keyword argument repeated: metaclass
     >>>
 
 Another way.
diff --git a/Lib/test/test_syntax.py b/Lib/test/test_syntax.py
index 128c4da..a7e7e2c 100644
--- a/Lib/test/test_syntax.py
+++ b/Lib/test/test_syntax.py
@@ -588,7 +588,7 @@
 >>> f(a=23, a=234)
 Traceback (most recent call last):
    ...
-SyntaxError: keyword argument repeated
+SyntaxError: keyword argument repeated: a
 
 >>> {1, 2, 3} = 42
 Traceback (most recent call last):