ci: Update action versions in push build workflow

ci: Update action versions in push build workflow

The workflow runs started issuing warnings because NodeJS 12 was
deprecated. Actions need to get updated to newer versions that use
NodeJS 16. This commit updates the `actions/checkout` and the
`actions/setup-java` actions to the latest version in the workflow that
builds on every push.

The new setup-java action requires the distribution to be specified,
since multiple JDK distributions are supported now. We chose Eclipse's
Temurin here which is the successor to AdoptOpenJDK, which we use for
development.