Fix changelog misformat

[uranusjr]

Fix #9815.

[webknjaz]

FYI this is how the default template looks now: https://github.com/twisted/towncrier/blob/master/src/towncrier/templates/default.rst

[pradyunsg]

@uranusjr if you're frustrated, would it help if I pick up this issue? I'm happy to, and it helps that I've been writing a bunch of Jinja templates lately.

[uranusjr]

Alright, this is the best I can do. The HTML is now correct, but the rendered NEWS.rst will now have a ton of blank lines between the version title and subsections:

.. towncrier release notes start

21.1.dev0 (2021-04-18)
======================



Process
-------
 
- Start installation scheme migration from ``distutils`` to ``sysconfig``. A

Every attempt I made trying to remove even one of them breaks the HTML.

[webknjaz]

RTD preview seems fine now and it's probably the main thing to care about right now. That jinja2 template can be edited later if someone is in the mood to entertain themself...

[uranusjr]

This is better than what we have in main now.

[webknjaz]

@uranusjr FYI apparently we still have a problem: #9828 (comment) / pypa/setuptools#2666