commit_graph: log lower level causes when logging to scuba

Summary: Calling `.to_string()` on `anyhow::Error` uses the `Display` trait which only displays the outermost error. Use `{:#}` instead to display the lower level causes as well.

Reviewed By: lmvasquezg

Differential Revision: D65816416

fbshipit-source-id: c149d1453376944fe99f664aac2fe4ad7574af26

eden/mononoke/repo_attributes/commit_graph/commit_graph/src/writer.rs

@@ -147,7 +147,7 @@ impl CommitGraphWriter for LoggingCommitGraphWriter {
 
         match self.inner_writer.add(ctx, cs_id, parents).try_timed().await {
             Err(err) => {
-                scuba.add("error", err.to_string());
+                scuba.add("error", format!("{:#}", err));
                 scuba.log_with_msg("Insertion failed", None);
 
                 Err(err)