Use the latest version of `gap-actions/build-pkg-docs`

[Joseph-Edwards]

The build-pkg-docs action was recently updated to v2.2.0, with a change that ensures that references to other manuals are relative (see gap-actions/build-pkg-docs#35).

We should make a new release that includes these changes to the manual.

[Joseph-Edwards]

I'm happy to make this release myself, with the blessing of a more seasoned Digraphs contributor. Perhaps @james-d-mitchell, @mtorpey or @wilfwilson?

[james-d-mitchell]

Go for it

[Joseph-Edwards]

Upon further inspection, since the last release, we have merged the PR Remove support for GAP 4.10 into the stable branch which breaks backwards compatibility (I think). I'll hold off on making a release for now until we have a discussion about version numbers and any other features that should go in the release.

[mtorpey]

Good call. @james-d-mitchell and I were talking this week about breaking changes, major version numbers and so on in regard to #824 and #825.