Upgrade Ubuntu image (needs sbt installed now) + actions

Upgrade Ubuntu image (needs sbt installed now) + actions

Install sbt

Switches to ubuntu-24.04 (from 20.04)

Also:
- Upgrades to actions/cache@v4 (from v3)
- Upgrades to peaceiris/actions-gh-pages@v4 (from v3)
- Upgrades to burrunan/gradle-cache-action@v2 (from v1)
- Upgrades gradle/wrapper-validation-action@v1 to gradle/actions/wrapper-validation@v4

Moving v4 tag to latest v4.1.1

Releasing v3.0.0, sets Java 17 as default

Support Asciidoctor Tabs

Block deprecated repos in /etc/hosts

Support Asciidoctor Tabs.

Improve Coursier cache