This uses the Jekyll Actions GitHub action to push the rendered docs to
the gh-pages branch rather than GitHub's automated docs flow. That will
allow greater control over how the docs are generated. Pushing to the
gh-pages branch only happens on pushes to main. For pull requests, the
docs are only built.
This tweaks the release GH workflow further so that it only triggers
when the `configure.ac` file (which owns the version) changes.
Plus it properly checkouts the PR branch to avoid wrongly looking
at a synthetic merge commit.
Dan Nicholson
Timothée Ravier
Colin Walters
Luca BRUNO