[3.10] Fix typos in the Lib directory (GH-28775) (GH-28804)

Fix typos in the Lib directory as identified by codespell.

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>.
(cherry picked from commit 745c9d9dfc1ad6fdfdf1d07420c6273ff67fa5be)

Co-authored-by: Christian Clauss <cclauss@me.com>
diff --git a/Lib/test/test_unparse.py b/Lib/test/test_unparse.py
index 9f67b49..33e1149 100644
--- a/Lib/test/test_unparse.py
+++ b/Lib/test/test_unparse.py
@@ -408,7 +408,7 @@ def test_type_ignore(self):
 
 
 class CosmeticTestCase(ASTTestCase):
-    """Test if there are cosmetic issues caused by unnecesary additions"""
+    """Test if there are cosmetic issues caused by unnecessary additions"""
 
     def test_simple_expressions_parens(self):
         self.check_src_roundtrip("(a := b)")