SonarQube 26.1 compatibility

[JuditKnoll]

This PR makes sure that SonarQube 26.1 is supported.

From SQ 26.1 release announcement:

The SonarQube Community Build runtime now requires Java Development Kit (JDK) 21 or a later version.

Using Java 21 required the following changes:

• mvn-compiler-plugin target and src to be set 8 from 7 in sample projects,
• update Scala version in sample projects (see Scala JDK compatibilty docs),
• gradle version upgrade in sample project to 8.5 (see Gradle Java compatibility docs),
  • gradle 8.5 required org.sonarqube gradle plugin upgrade (see [sonarqube 4.0 introducing support for gradle 8].(https://github.com/SonarSource/sonar-scanner-gradle/releases/tag/4.0))

In the multi-module sample project for maven the src and target was set, but not for gradle, which resulted in a missing SIC_INNER_SHOULD_BE_STATIC hit, as inner classes are compiled a bit differently with different java versions.