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/gpui/src/shared_string.rs

@@ -27,8 +27,8 @@ impl JsonSchema for SharedString {
         String::schema_name()
     }
 
-    fn json_schema(gen: &mut schemars::gen::SchemaGenerator) -> schemars::schema::Schema {
-        String::json_schema(gen)
+    fn json_schema(r#gen: &mut schemars::r#gen::SchemaGenerator) -> schemars::schema::Schema {
+        String::json_schema(r#gen)
     }
 }