fix typo (#3642)

Author: mairaw

xml/System.Windows.Forms/ContainerControl.xml

@@ -361,7 +361,7 @@
   
  ]]></format>
         </remarks>
-        <exception cref="T:System.ComponentModel.InvalidEnumArgumentException">A <see cref="T:System.Windows.Forms.AutoValidate" /> value that is not valid was used to set this property.</exception>
+        <exception cref="T:System.ComponentModel.InvalidEnumArgumentException">An <see cref="T:System.Windows.Forms.AutoValidate" /> value that is not valid was used to set this property.</exception>
         <altmember cref="T:System.Windows.Forms.AutoValidate" />
         <altmember cref="Overload:System.Windows.Forms.ContainerControl.Validate" />
         <altmember cref="E:System.Windows.Forms.ContainerControl.AutoValidateChanged" />