Fixed wrong expectation in unit test.

Signed-off-by: Juergen Fickel <juergen.fickel@bosch.io>

internal/utils/tracing/src/test/java/org/eclipse/ditto/internal/utils/tracing/DittoTracingTest.java

@@ -138,7 +138,7 @@ public void newPreparedSpanWithNullOperationNameThrowsNullPointerException() {
 
         assertThatNullPointerException()
                 .isThrownBy(() -> DittoTracing.newPreparedSpan(Map.of(), null))
-                .withMessage("The traceOperationName must not be null!")
+                .withMessage("The operationName must not be null!")
                 .withNoCause();
     }