infra: avoid maven warnings

[Bananeweizen]

Use the release property instead of source and target for compilation.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[Bananeweizen]

That avoids these warnings:

Also remove the property java.version as that is the name of a pre-defined property injected into the maven properties, containing the actual JDK runtime version (like 21.0.1). It's really confusing to override that injected property, and could potentially lead to errors at other locations.