make AbstractIcebergTest class public to avoid javadoc error

Author: ghareeb-falazi

instrumentation/iceberg-1.8/testing/src/main/java/io/opentelemetry/instrumentation/iceberg/v1_8/AbstractIcebergTest.java

@@ -34,7 +34,7 @@
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 
-abstract class AbstractIcebergTest {
+public abstract class AbstractIcebergTest {
   protected static final int FORMAT_VERSION = 2;
   protected static final Schema SCHEMA =
       new Schema(