Fix fieldtrial testing config for stage 2 of ButterForPayments

This CL enables AutofillEnablePasswordInfoBarAccountIndicationFooter
(in addition to the existing config), to match the actual config that
we intend to launch. (This should've been part of the previous CL,
https://crrev.com/c/2595742, but I missed it there)

Bug: 1121258
Change-Id: Id9852a09b719e99aea517cb3a1db846f42e06dde
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2617843
Auto-Submit: Marc Treib <treib@chromium.org>
Commit-Queue: Anne Lim <annelim@google.com>
Reviewed-by: Anne Lim <annelim@google.com>
Cr-Commit-Position: refs/heads/master@{#841663}

testing/variations/fieldtrial_testing_config.json

@@ -1376,7 +1376,8 @@
                 {
                     "name": "Enabled_Stage2",
                     "enable_features": [
-                        "AutofillEnableAccountWalletStorage"
+                        "AutofillEnableAccountWalletStorage",
+                        "AutofillEnablePasswordInfoBarAccountIndicationFooter"
                     ],
                     "disable_features": [
                         "WalletRequiresFirstSyncSetupComplete"