Correct the enabled group name for DownloadWithServicificationM77

The group name has been changed to Enabled_20191111 some time back

Change-Id: Ifb62c159f9ac02d21bece604e17ccb22e3464b91
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2002744Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732581}

testing/variations/fieldtrial_testing_config.json

@@ -2374,7 +2374,7 @@
             ],
             "experiments": [
                 {
-                    "name": "Enabled",
+                    "name": "Enabled_20191111",
                     "enable_features": [
                         "ServiceManagerForDownload"
                     ]