scala/scala3#8661

without this fix, this spec will fail:
akka-actor-typed-tests/testOnly akka.actor.typed.TransformMessagesJavaBehaviorSpec

Author: giabao

akka-actor/src/main/java/akka/japi/pf/AbstractPFBuilder.java

@@ -12,7 +12,9 @@
  * @param <F> the input type, that this PartialFunction will be applied to
  * @param <T> the return type, that the results of the application will have
  */
-abstract class AbstractPFBuilder<F, T> {
+// todo remove `public` when this issue is fix:
+// https://github.com/lampepfl/dotty/issues/8661
+public abstract class AbstractPFBuilder<F, T> {
 
   protected PartialFunction<F, T> statements = null;