Reduce serializability of project delete (#11628)

This may reduce locks when deleting projects.

Release Notes:

- N/A

crates/collab/src/db.rs

@@ -415,7 +415,7 @@ impl Database {
         if is_serialization_error(error) && prev_attempt_count < SLEEPS.len() {
             let base_delay = SLEEPS[prev_attempt_count];
             let randomized_delay = base_delay * self.rng.lock().await.gen_range(0.5..=2.0);
-            log::info!(
+            log::warn!(
                 "retrying transaction after serialization error. delay: {} ms.",
                 randomized_delay
             );