Fix build with JDK >= 20 when option -Dbytecode.version is not provided

[Godin]

Due to https://bugs.openjdk.org/browse/JDK-8173605 currently the execution of build with JDK 20 and higher requires specification of -Dbytecode.version, ie execution of mvn clean package -Dbytecode.version=8 succeeds, whereas execution of mvn clean package fails

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.11.0:compile (default-compile) on project org.jacoco.core: Compilation failure: Compilation failure:
[ERROR] Source option 7 is no longer supported. Use 8 or later.
[ERROR] Target option 7 is no longer supported. Use 8 or later.