Add news item.

I'm not sure this is worth a news item, though.

Author: bitdancer

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

@@ -0,0 +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
+of the mailbox accessed through that header object would result in an
+`IndexError`. It now correctly returns an empty string as the result.