Fix code blocks in CHANGELOG.md (#724)

Previously the mixed single/double backtick usage meant
the code block didn't end at the correct location and instead
ran into the normal text.

Author: edmorley

CHANGELOG.rst

@@ -11,7 +11,7 @@ Changelog
 * Introduce ``metadata.Metadata`` (along with ``metadata.ExceptionGroup`` and ``metadata.InvalidMetadata``; :issue:`570`)
 * Introduce the ``validate`` keyword parameter to ``utils.validate_name()`` (:issue:`570`)
 * Introduce ``utils.is_normalized_name()`` (:issue:`570`)
-* Make ``utils.parse_sdist_filename()` and ``utils.parse_wheel_filename()`
+* Make ``utils.parse_sdist_filename()`` and ``utils.parse_wheel_filename()``
   raise ``InvalidSdistFilename`` and ``InvalidWheelFilename``, respectively,
   when the version component of the name is invalid