Python 3.13: Replace deprecated makeSuite() (#65)

The function has been deprecated in Python 3.11 and is no longer
available in Python 3.13.

testgrey.py

@@ -35,7 +35,7 @@ class GreylistTestCase(unittest.TestCase):
     # new one past expire
     rc = grey.check('1.2.3.5','foo@bar.com','baz@spat.com',timeinc=6*3600)
     self.assertEqual(rc,0)
-    # original past retain 
+    # original past retain
     rc = grey.check('1.2.3.4','foo@bar.com','baz@spat.com',timeinc=37*24*3600)
     self.assertEqual(rc,0)
     # new one for testing expire
@@ -48,8 +48,8 @@ class GreylistTestCase(unittest.TestCase):
     self.assertEqual(rc,1)
     grey.close()
 
-def suite(): 
-  s = unittest.makeSuite(GreylistTestCase,'test')
+def suite():
+  s = unittest.TestLoader().loadTestsFromTestCase(GreylistTestCase)
   return s
 
 if __name__ == '__main__':