📦 🔁 themes: Synchronize git submodule with remote

This commit updates the git submodule with @MuluhGodson's changes added
in unicef/inventory-hugo-theme#4. Articles can now support front matter
for their categories, and articles sharing the same category may appear
as related articles at the bottom of the page.

Part of #12, but does not yet close it.

Signed-off-by: Justin W. Flory (he/him) [UNICEF Innovation] <jflory@unicef.org>