Avoid creating more than one log subscriber (when integration tests are running)

backend/src/log.rs

@@ -94,9 +94,16 @@ impl Log {
             .with_thread_ids(TRACING_DISPLAY_THREAD)
             .with_thread_names(TRACING_DISPLAY_THREAD);
 
-        tracing_subscriber::Registry::default()
+        if let Err(error) = tracing_subscriber::Registry::default()
             .with(layer_stdout)
-            .init();
+            .try_init()
+        {
+            // It happens during the integration tests.
+            eprintln!(
+                "Error during initialization of the tracing subscriber: {}",
+                error
+            );
+        }
 
         Log::StdoutOnly
     }