fix: Ignore JDK 8-only warning

When compiling with JDK 8 an "unknown enum constant java.lang.annotation.ElementType.MODULE" warning appears.

Author: ppkarwasz

log4j-core-test/src/test/java/org/apache/logging/log4j/core/config/plugins/processor/GraalVmProcessorTest.java

@@ -274,6 +274,8 @@ private static List<String> generateDescriptor(
         return diagnosticCollector.getDiagnostics().stream()
                 .filter(d -> d.getKind() != Diagnostic.Kind.NOTE)
                 .map(d -> d.getMessage(Locale.ROOT))
+                // This message appears when the test runs on JDK 8
+                .filter(m -> !"unknown enum constant java.lang.annotation.ElementType.MODULE".equals(m))
                 .collect(Collectors.toList());
     }
 }