fix instances of consecutive articles (closes #23221)

Patch by Karan Goel.
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index 98ccfe4..1164f3f 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -644,7 +644,7 @@
 
 
 class TestOptionalsRequired(ParserTestCase):
-    """Tests the an optional action that is required"""
+    """Tests an optional action that is required"""
 
     argument_signatures = [
         Sig('-x', type=int, required=True),