Docs/build update stuff

[briantist]

SUMMARY

Some stuff taken from #260

• update the workflow dependency
• update the preview stuff (committed antsibull-docs sphinx-init output)
• exclude sphinx .post0 release due to https://github.com/ansible-community/antsibull-docs/issues/39

Merging will fix the currently broken docs build; it will fail in this PR in the "base" build due this not being in main yet. Validate ~should pass~ will not pass because with the change to use 2.14 for docs builds, the missing filter documentation is now a fatal error.

~I'm going to merge these changes first so that the base docs build in #260 can pass.~

Actually.. the base build will still fail because of the missing filter docs I suppose.. oof. Am going to just close this and do everything in the other one I guess.

ISSUE TYPE

• Docs Pull Request

[briantist]

hm maybe I was wrong about the build, let's merge this and see