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/llm/authorization.rs

@@ -193,7 +193,9 @@ mod tests {
                 .to_vec();
             assert_eq!(
                 String::from_utf8(response_body).unwrap(),
-                format!("access to {provider:?} models is not available in your region ({country_code})")
+                format!(
+                    "access to {provider:?} models is not available in your region ({country_code})"
+                )
             );
         }
     }

crates/collab/src/llm/db/tests.rs

@@ -26,7 +26,7 @@ impl TestLlmDb {
         let mut rng = StdRng::from_entropy();
         let url = format!(
             "postgres://postgres@localhost/zed-llm-test-{}",
-            rng.gen::<u128>()
+            rng.r#gen::<u128>()
         );
         let runtime = tokio::runtime::Builder::new_current_thread()
             .enable_io()