Add missing awaits (#15595)

packages/flutter_tools/lib/src/android/android_workflow.dart

@@ -225,10 +225,10 @@ class AndroidWorkflow extends DoctorValidator implements Workflow {
       environment: androidSdk.sdkManagerEnv,
     );
 
-    waitGroup<Null>(<Future<Null>>[
+    process.stdin.addStream(stdin);
+    await waitGroup<Null>(<Future<Null>>[
       stdout.addStream(process.stdout),
       stderr.addStream(process.stderr),
-      process.stdin.addStream(stdin),
     ]);
 
     final int exitCode = await process.exitCode;

packages/flutter_tools/lib/src/base/process.dart

@@ -194,7 +194,7 @@ Future<int> runInteractively(List<String> command, {
   process.stdin.addStream(stdin);
   // Wait for stdout and stderr to be fully processed, because process.exitCode
   // may complete first.
-  Future.wait<dynamic>(<Future<dynamic>>[
+  await Future.wait<dynamic>(<Future<dynamic>>[
     stdout.addStream(process.stdout),
     stderr.addStream(process.stderr),
   ]);