09-coap: pass URI instead of separate host and path components

adapts the release spec to the changes from RIOT-OS/RIOT#20554

09-coap/test_spec09.py

@@ -36,7 +36,7 @@ def coap_get(
         cmd = "coap get "
         if confirmable:
             cmd += "-c "
-        cmd += f"[{addr}]:{port:d} {resource}"
+        cmd += f"coap://[{addr}]:{port:d}{resource}"
         return self.cmd(cmd, timeout=timeout, async_=async_)