Fix Java 8 building and publishing

[wmdietl]

A project that consumes Java 8 artifacts failed with:

* What went wrong:
Execution failed for task ':compileJava'.
> Could not resolve all files for configuration ':compileClasspath'.
   > Could not resolve io.github.eisop:checker:3.49.5-eisop2-SNAPSHOT.
     Required by:
         project :
      > Dependency resolution is looking for a library compatible with JVM runtime version 8, but 'io.github.eisop:checker:3.49.5-eisop2-SNAPSHOT' is only compatible with JVM runtime version 25 or newer.

* Try:
> Change the dependency on 'io.github.eisop:checker:3.49.5-eisop2-SNAPSHOT' to an earlier version that supports JVM runtime version 25.
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Run with --scan to get full insights.
> Get more help at https://help.gradle.org.

The first commit changed this to:

Execution failed for task ':compileJava'.
> Could not resolve all files for configuration ':compileClasspath'.
   > Could not resolve io.github.eisop:checker:3.49.5-eisop2-SNAPSHOT.
     Required by:
         project :
      > No matching variant of io.github.eisop:checker:3.49.5-eisop2-SNAPSHOT was found. The consumer was configured to find a library for use during compile-time, compatible with Java 8, preferably in the form of class files, preferably optimized for standard JVMs, and its dependencies declared externally but:
          - Variant 'shadowRuntimeElements' declares a library, compatible with Java 8, packaged as a jar, and its dependencies repackaged (shadow jar):
              - Incompatible because this component declares a component for use during 'shadow-runtime-elements' and the consumer needed a component for use during compile-time
              - Other compatible attribute:
                  - Doesn't say anything about its target Java environment (preferred optimized for standard JVMs)

* Try:
> No matching variant errors are explained in more detail at https://docs.gradle.org/8.9/userguide/variant_model.html#sub:variant-no-match.
> Review the variant matching algorithm at https://docs.gradle.org/8.9/userguide/variant_attributes.html#sec:abm_algorithm.

With both commits this works again.

However:

• We need a test case for this.
• Is this the right fix?