Invert the pytorch selector image too

Signed-off-by: Michał Górny <mgorny@quansight.com>

Author: mgorny

peps/pep-0817.rst

@@ -164,6 +164,7 @@ example of PyTorch, while the problem, the workarounds, and the impact
 on users also apply to other packages.
 
 .. figure:: pep-0817/pytorch_variant_selector.png
+    :class: invert-in-dark-mode
     :alt: A grid-based selector for PyTorch versions. Individual rows
           provide the choice of PyTorch Build (stable or nightly),
           operating system (Linux, Mac, Windows), package (Pip,