fix: drop temp tag after doc insert (#1810)

## Description

When importing files into docs, the temp tag should only be dropped
*after* the hash was inserted into the doc. Otherwise gc could
potentially delete the blob if hitting in between the tag drop and the
completion of the doc insert.

iroh/src/node.rs

@@ -1038,7 +1038,6 @@ impl<D: BaoStore> RpcHandler<D> {
 
         let hash_and_format = temp_tag.inner();
         let HashAndFormat { hash, .. } = *hash_and_format;
-        drop(temp_tag);
         self.inner
             .sync
             .doc_set_hash(DocSetHashRequest {
@@ -1049,6 +1048,7 @@ impl<D: BaoStore> RpcHandler<D> {
                 size,
             })
             .await?;
+        drop(temp_tag);
         progress.send(DocImportProgress::AllDone { key }).await?;
         Ok(())
     }