Disable some plain Python (non Cython related) tests that fail in Py3.10 due...

Disable some plain Python (non Cython related) tests that fail in Py3.10 due to changed error messages.

tests/run/test_exceptions.pyx

@@ -26,7 +26,7 @@ except ImportError:
 
 no_tracing = unittest.skip("For nested functions, Cython generates a C call without recursion checks.")
 
-cpython_only = unittest.skip("Tests for _testcapi make no sense here.")
+cpython_only = unittest.skip("Tests for _testcapi or Python error messages make no sense here.")
 
 
 class NaiveException(Exception):
@@ -143,6 +143,7 @@ class ExceptionTests(unittest.TestCase):
 
         self.raise_catch(StopAsyncIteration, "StopAsyncIteration")
 
+    @cpython_only
     def testSyntaxErrorMessage(self):
         # make sure the right exception message is raised for each of
         # these code fragments
@@ -165,6 +166,7 @@ class ExceptionTests(unittest.TestCase):
         ckmsg(s, "'continue' not properly in loop")
         ckmsg("continue\n", "'continue' not properly in loop")
 
+    @cpython_only
     def testSyntaxErrorMissingParens(self):
         def ckmsg(src, msg, exception=SyntaxError):
             try:
@@ -193,6 +195,7 @@ class ExceptionTests(unittest.TestCase):
         s = '''if True:\n        print()\n\texec "mixed tabs and spaces"'''
         ckmsg(s, "inconsistent use of tabs and spaces in indentation", TabError)
 
+    @cpython_only
     def testSyntaxErrorOffset(self):
         def check(src, lineno, offset):
             with self.assertRaises(SyntaxError) as cm: