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/tests/integration_tests.rs

@@ -5103,7 +5103,9 @@ async fn test_project_search(
                 results.entry(buffer).or_insert(ranges);
             }
             SearchResult::LimitReached => {
-                panic!("Unexpectedly reached search limit in tests. If you do want to assert limit-reached, change this panic call.")
+                panic!(
+                    "Unexpectedly reached search limit in tests. If you do want to assert limit-reached, change this panic call."
+                )
             }
         };
     }
@@ -5602,7 +5604,7 @@ async fn test_open_buffer_while_getting_definition_pointing_to_it(
 
     let definitions;
     let buffer_b2;
-    if rng.gen() {
+    if rng.r#gen() {
         definitions = project_b.update(cx_b, |p, cx| p.definition(&buffer_b1, 23, cx));
         (buffer_b2, _) = project_b
             .update(cx_b, |p, cx| {