Update code block reference in Custom Activities topic

The reference to the code block in the Custom Activities article was corrected. Instead of pointing to 'PrintMessageActivity.cs', it now correctly points to 'PrintMessageCodeActivity.cs'. This change ensures the right example code is displayed for the CodeActivity section.

writerside/topics/Custom-Activities.topic

@@ -67,7 +67,7 @@
         <chapter title="Activity vs CodeActivity" id="activity-vs-code-activity">
             <p>When your custom activity's workflow is straightforward and concludes immediately after its task, inheriting from <code>CodeActivity</code> offers a streamlined approach. This base class is engineered to automatically signal the completion of the activity post-execution, eliminating the need for explicit completion logic.</p>
             <p>To illustrate, let's revisit the <code>PrintMessage</code> activity, this time reimagined using <code>CodeActivity</code> as its base. This example underscores the absence of manual completion:</p>
-            <code-block lang="c#" src="extensibility/custom-activities/PrintMessageActivity.cs"/>
+            <code-block lang="c#" src="extensibility/custom-activities/PrintMessageCodeActivity.cs"/>
             <p>This approach allows developers to focus on the core logic of their activities without worrying about activity completion.</p>
         </chapter>