docs: correct invalid <CODE_BLOCK_5> placeholder to <CODE_BLOCK>

Author: ricardohsmello

docs/challenge/network.mdx

@@ -17,7 +17,7 @@ from datetime import datetime, timedelta
 # Calculate the date and time 24 hours from now
 delete_after = (datetime.utcnow() + timedelta(hours=24)).isoformat() + 'Z'
 
-!atlas accessLists <CODE_BLOCK_5>
+!atlas accessLists <CODE_BLOCK>
 ```
 
 :::tip