bpo-42770: Fix a typo in the email.headerregistry docs (GH-23982)



Automerge-Triggered-By: GH:zware
diff --git a/Doc/library/email.headerregistry.rst b/Doc/library/email.headerregistry.rst
index 9376da2..3e1d97a 100644
--- a/Doc/library/email.headerregistry.rst
+++ b/Doc/library/email.headerregistry.rst
@@ -289,7 +289,7 @@
     A :class:`ParameterizedMIMEHeader` class that handles the
     :mailheader:`Content-Disposition` header.
 
-    .. attribute:: content-disposition
+    .. attribute:: content_disposition
 
        ``inline`` and ``attachment`` are the only valid values in common use.