Never run transactions using serializable isolation (#33780)

We believe this is causing the database to execute certain queries very
slowly, and it's unclear whether we're actually benefitting from it.

Release Notes:

- N/A

crates/collab/src/db/queries/projects.rs

@@ -112,7 +112,7 @@ impl Database {
     }
 
     pub async fn delete_project(&self, project_id: ProjectId) -> Result<()> {
-        self.weak_transaction(|tx| async move {
+        self.transaction(|tx| async move {
             project::Entity::delete_by_id(project_id).exec(&*tx).await?;
             Ok(())
         })