`java-version` property of `actions/setup-java` not fully mimicked

[Stephan202]

If one passes multiple Java versions to actions/setup-java's java-version property, then ~/.m2/toolchains.xml is configured to reference all these versions. However, when s4u/setup-maven-action is used, only the Java version listed first is added to the Maven Toolchains configuration.

To observe the issue, consider this change and observe the result of cat ~/.m2/toolchains.xml before and after the change.