Run akka-remote tests on Scala 3 (#30415)

* Run akka-remote tests on Scala 3

* Test the same scenario on Scala 2.13 and 3

A case object is `Serializable` on Scala 3 but not on Scala 2.13, so
this test would fail because no serializer is found on Scala 2.13,
and because the Java serializer is disabled on Scala 3.

By using a class instead, which is not `Serializable` both on Scala 2.13
and Scala 3, we test the same thing on both Scala versions.

.github/workflows/scala3-build.yml

@@ -34,14 +34,16 @@ jobs:
             akka-actor-testkit-typed/test \
             akka-actor-typed/compile \
             akka-actor-typed-tests/test \
+            akka-coordination/test \
             akka-discovery/test \
             akka-pki/test \
             akka-protobuf/test \
             akka-protobuf-v3/test \
-            akka-slf4j/test \akka-stream/test \
-            akka-stream-tests-tck/test \
-            akka-coordination/test \
             akka-serialization-jackson/test:compile \
-            akka-testkit/test \
+            akka-slf4j/test \
+            akka-stream/test \
             akka-stream-testkit/test \
-            akka-remote/compile
+            akka-stream-tests-tck/test \
+            akka-remote/test \
+            akka-remote-tests/test \
+            akka-testkit/test