Fixes future warning for awaiting Future returns in async bodies inside try blocks (#9664)

* fixes future warning for `await`ing `Future` returns in `async` bodies inside `try` blocks

* fixes new diagnostic

Author: FMorschel

packages/devtools_app_shared/lib/src/service/eval_on_dart_library.dart

@@ -211,7 +211,7 @@ class EvalOnDartLibrary extends DisposableController
       if (result is ErrorRef) {
         throw result;
       }
-      return result as FutureOr<InstanceRef?>;
+      return await (result as FutureOr<InstanceRef?>);
     } catch (e, stack) {
       if (shouldLogError) {
         _handleError('$e - $expression', stack);
@@ -242,7 +242,7 @@ class EvalOnDartLibrary extends DisposableController
       if (result is ErrorRef) {
         throw result;
       }
-      return result as FutureOr<InstanceRef?>;
+      return await (result as FutureOr<InstanceRef?>);
     } catch (e, stack) {
       if (shouldLogError) {
         _handleError('$e - $name', stack);

packages/devtools_shared/test/helpers/helpers.dart

@@ -55,7 +55,7 @@ Future<TestDtdConnectionInfo> startDtd() async {
       }
     });
 
-    return completer.future
+    return await completer.future
         .timeout(dtdConnectTimeout, onTimeout: onFailure)
         .then((value) async {
       await dtdStoutSubscription?.cancel();