Fix delayed missing-fields diagnostics after rebase

Use the current type-owner variable when emitting delayed missing-fields diagnostics after the upstream diagnostics plumbing rename.

AI assistance disclosure: ChatGPT helped identify and validate this minimal compile fix. I reviewed the change before committing.

Author: Twil3akine

crates/hir/src/lib.rs

@@ -2199,7 +2199,7 @@ impl DefWithBody {
                 d,
                 source_map,
                 sig_source_map,
-                env,
+                type_owner,
             ));
         }