timeline: lower log severity of read receipts issues

Those two issues really aren't errors we should be too scared of:

- on the one hand, they don't prevent correct usage of the timeline, but
slightly decrease the UX's quality
- on the other hand, they may indicate that read receipts haven't been
received yet, OR some events are unknown (can be happening if the
previous read receipt refers to an event the timeline doesn't know
about).

So I lowered their severity to debug instead of error, since only
outstanding issues should errors or warnings in my opinion.

crates/matrix-sdk-ui/src/timeline/read_receipts.rs

@@ -24,7 +24,7 @@ use ruma::{
     events::receipt::{Receipt, ReceiptEventContent, ReceiptThread, ReceiptType},
     EventId, OwnedEventId, OwnedUserId, UserId,
 };
-use tracing::{error, warn};
+use tracing::{debug, error, warn};
 
 use super::{
     inner::{
@@ -282,7 +282,7 @@ impl ReadReceiptTimelineUpdate {
         };
 
         let Some((receipt_pos, event_item)) = rfind_event_by_id(items, event_id) else {
-            error!(%event_id, %user_id, "inconsistent state: old event item for read receipt was not found");
+            debug!(%event_id, %user_id, "inconsistent state: old event item for read receipt was not found");
             return;
         };
 
@@ -291,7 +291,7 @@ impl ReadReceiptTimelineUpdate {
 
         if let Some(remote_event_item) = event_item.as_remote_mut() {
             if remote_event_item.read_receipts.swap_remove(user_id).is_none() {
-                error!(
+                debug!(
                     %event_id, %user_id,
                     "inconsistent state: old event item for user's read \
                      receipt doesn't have a receipt for the user"