Fixed docs build with sphinxcontrib-spelling 7.5.0+.

sphinxcontrib-spelling 7.5.0+ includes captions of figures in the set
of nodes for which the text is checked.

docs/internals/howto-release-django.txt

@@ -63,7 +63,7 @@ You'll need a few things before getting started:
 * Access to Django's record on PyPI. Create a file with your credentials:
 
   .. code-block:: ini
-    :caption: ~/.pypirc
+    :caption: ``~/.pypirc``
 
     [pypi]
     username:YourUsername