Antora (#462)

* Use providers.provider for modifiedFile

This defers the looking up of modifiedFiles until it is used. It
also allows other tasks to be ran from the non-primary worktree.
Working in another worktree is essential for Antora which will clone
each branch/tag into a new worktree to process it.

* Move Asdiidoc Attributes to antora.yml

This ensures the attributes are available for the docs-build branch
as well.

* Fix GitHub Actions Permissions

The permission actions: write is necessary so that pushes to branches
and tags can invoke the deploy-docs workflow on the docs-build branch

.github/workflows/deploy-docs-antora.yml

@@ -4,7 +4,8 @@ on:
     branches-ignore: [ gh-pages ]
     tags: '**'
   workflow_dispatch:
-permissions: read-all
+permissions:
+  actions: write
 jobs:
   build:
     runs-on: ubuntu-latest