[FedCM] Rename "phone" to "tel"

This matches HTML5, per recommendation from the TAG.

See:
w3c-fedid/FedCM#435 (comment)

Bug: 382086282
Change-Id: If04f3e7f0d838e293dd0b9404e3012de43af99e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6479016
Reviewed-by: Nicolás Peña <npm@chromium.org>
Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1450201}

Author: cbiesinger

fedcm/support/single_identifier_accounts.py

@@ -17,7 +17,7 @@ def main(request, response):
   },
   {
    "id": "john_doe2",
-   "phone": "+1 (416) 000-0000"
+   "tel": "+1 (416) 000-0000"
   }
   ]
 }