Published artifacts have class file version incompatible with JDK 8

Is the library really using a Java feature that requires JDK > 8?

> [error]   bad class file: /home/runner/.cache/coursier/v1/https/repo1.maven.org/maven2/com/pi4j/pi4j-core/1.4/pi4j-core-1.4.jar(com/pi4j/io/gpio/Pin.class)
> [error]     class file has wrong version 55.0, should be 52.0

If not, you should build the published artifacts with `-target 8` so they can be used under JDK 8.