[AF] Add AutofillCreditCardAuthentication to Clank fieldtrial_tst._cfg.

Change-Id: Ica35f3494f4bbeae333f777e75b026832f5dc82a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2410928Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Jared Saul <jsaul@google.com>
Cr-Commit-Position: refs/heads/master@{#806823}

testing/variations/fieldtrial_testing_config.json

@@ -669,6 +669,22 @@
             ]
         }
     ],
+    "AutofillCreditCardAuthentication": [
+        {
+            "platforms": [
+                "android",
+                "android_webview"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "AutofillCreditCardAuthentication"
+                    ]
+                }
+            ]
+        }
+    ],
     "AutofillEnableCardNicknameManagementAndUpstream": [
         {
             "platforms": [