adapter: avoid more tracing ref panics in explain codepaths

Author: guswynn

src/adapter/src/coord/sequencer/inner.rs

@@ -3434,6 +3434,7 @@ impl Coordinator {
                     &source_ids,
                     None, // no real-time recency
                 )
+                .with_subscriber(root_dispatch.clone())
                 .await?
                 .timestamp_context;
 

src/adapter/src/coord/sequencer/old_optimizer_api.rs

@@ -1024,6 +1024,7 @@ impl Coordinator {
                 &source_ids,
                 None, // no real-time recency
             )
+            .with_subscriber(root_dispatch.clone())
             .await?
             .timestamp_context;