chore: Prepare for Rust edition bump to 2024 (without autofix) (#27791)

Successor to #27779 - in this PR I've applied changes manually, without
futzing with if let lifetimes at all.

Release Notes:

- N/A

crates/collab/src/db/tests.rs

@@ -74,7 +74,7 @@ impl TestDb {
         let mut rng = StdRng::from_entropy();
         let url = format!(
             "postgres://postgres@localhost/zed-test-{}",
-            rng.gen::<u128>()
+            rng.r#gen::<u128>()
         );
         let runtime = tokio::runtime::Builder::new_current_thread()
             .enable_io()