Reapply "refactor: @JMeterSerialTest.java -> JMeterSerialTest.kt"

This reverts commit 241078e51874a7cf8347437fc029a649cd223705.
diff --git a/src/jorphan/src/testFixtures/java/org/apache/jorphan/test/JMeterSerialTest.java b/src/jorphan/src/testFixtures/kotlin/org/apache/jorphan/test/JMeterSerialTest.kt
similarity index 100%
rename from src/jorphan/src/testFixtures/java/org/apache/jorphan/test/JMeterSerialTest.java
rename to src/jorphan/src/testFixtures/kotlin/org/apache/jorphan/test/JMeterSerialTest.kt