Upgrade various GitHub actions we depend on

Moving v4 tag to latest v4.1.2

Upgrade various GitHub actions we depend on

Moving v3 tag to latest v3.6.1

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

Releasing v3.0.0, sets Java 17 as default

Support Asciidoctor Tabs

Block deprecated repos in /etc/hosts