Fix mdns client example shutdown sequence. (#25889)

Shutting down the platform manager while the event loop is not fully shut down
(which is the case when StopEventLoopTask is called from inside the event loop
itself) is not supported.

Fixes #8917

examples/minimal-mdns/client.cpp

@@ -342,7 +342,6 @@ int main(int argc, char ** args)
             gMdnsServer.Shutdown();
 
             DeviceLayer::PlatformMgr().StopEventLoopTask();
-            DeviceLayer::PlatformMgr().Shutdown();
         },
         nullptr);
     if (err != CHIP_NO_ERROR)
@@ -352,6 +351,9 @@ int main(int argc, char ** args)
 
     DeviceLayer::PlatformMgr().RunEventLoop();
 
+    DeviceLayer::PlatformMgr().Shutdown();
+    Platform::MemoryShutdown();
+
     printf("Done...\n");
     return 0;
 }