Fix Sphinx syntax in news item.

Author: bitdancer

Misc/NEWS.d/next/Library/2026-04-13-15-59-44.gh-issue-148518.RQdvsu.rst

@@ -1,4 +1,4 @@
 If an email containing an address header that ended in an open double quote
-was parsed with a non-`compat32` policy, accessing the `username` attribute
+was parsed with a non-``compat32`` policy, accessing the ``username`` attribute
 of the mailbox accessed through that header object would result in an
-`IndexError`. It now correctly returns an empty string as the result.
+``IndexError``. It now correctly returns an empty string as the result.