Fix changelog fragment formatting

Add blank line before the attribution line.

Author: julianz-

docs/changelog-fragments.d/820.contrib.rst

@@ -2,4 +2,5 @@ Refactored ``_from_server_socket()`` in :py:class:`~cheroot.connections.Connecti
 This function had become highly nested and complex, triggering
 linter warnings (C901, WPS505). Decomposed the logic into
 several smaller private methods.
+
 -- by :user:`julianz-`