Fix iOS automatic signing on buildbots. (#14024)

dev/devicelab/lib/tasks/hot_mode_tests.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
+import 'package:flutter_devicelab/framework/ios.dart';
 import 'package:path/path.dart' as path;
 
 import '../framework/adb.dart';
@@ -33,6 +34,9 @@ TaskFunction createHotModeTest({ bool isPreviewDart2: false }) {
       mkdirs(_editedFlutterGalleryDir);
       recursiveCopy(flutterGalleryDir, _editedFlutterGalleryDir);
       await inDirectory(_editedFlutterGalleryDir, () async {
+        if (deviceOperatingSystem == DeviceOperatingSystem.ios)
+          await prepareProvisioningCertificates(_editedFlutterGalleryDir.path);
+
         final Process process = await startProcess(
           path.join(flutterDirectory.path, 'bin', 'flutter'),
           <String>['run']..addAll(options),