Fix 0.22.3 manpages not appearing in the doc index

Summary:
D7771 needs to be cherry-picked so that the version number is set correctly
in the manpages' frontmatter, which affects the manpage link generation.

Test Plan:

./fetch_documentation.sh
make serve

Navigate to http://localhost:4000/doc/ and verify 0.22.3 has a link to its manpages as expected

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7772