Async drop source info fix for proxy-drop-coroutine - fixes crash at debug info generation

Author: azhogin

compiler/rustc_middle/src/ty/mod.rs

@@ -1934,7 +1934,7 @@ impl<'tcx> TyCtxt<'tcx> {
                     field_tys: [].into(),
                     field_names: [].into(),
                     variant_fields,
-                    variant_source_info: [source_info].into(),
+                    variant_source_info: [source_info, source_info, source_info].into(),
                     storage_conflicts: BitMatrix::new(0, 0),
                 };
                 return Some(self.arena.alloc(proxy_layout));