[3.8] Fix typos in docs, comments and test assert messages (GH-14872). (#14900)

(cherry picked from commit 96e12d5f4f3c5a20986566038ee763dff3c228a1)

Co-authored-by: Min ho Kim <minho42@gmail.com>
diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index cb0e18c..facf9d2 100755
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -3043,11 +3043,11 @@
     def test_non_identifier_field_names(self):
         for field in ['()', 'x,y', '*', '2@3', '', 'little johnny tables']:
             with self.subTest(field=field):
-                with self.assertRaisesRegex(TypeError, 'must be valid identifers'):
+                with self.assertRaisesRegex(TypeError, 'must be valid identifiers'):
                     make_dataclass('C', ['a', field])
-                with self.assertRaisesRegex(TypeError, 'must be valid identifers'):
+                with self.assertRaisesRegex(TypeError, 'must be valid identifiers'):
                     make_dataclass('C', [field])
-                with self.assertRaisesRegex(TypeError, 'must be valid identifers'):
+                with self.assertRaisesRegex(TypeError, 'must be valid identifiers'):
                     make_dataclass('C', [field, 'a'])
 
     def test_underscore_field_names(self):