Investigate why 429's on Sign Transaction are causing a Sentry alert

[piyalbasu]

A specific user has been running into 429's and opening the sign transaction view, which leads to an inability to fetch account balances. With a recent change, we are gracefully handling this error, yet Sentry is still alerting on this. Let's investigate why this is the case and potentially tune our alerting if this truly is a false positive

Sentry alert: https://stellarorg.sentry.io/issues/7317156849/?referrer=slack&notification_uuid=1bd8be11-cbcb-445f-b580-83f53d8d9d91&alert_rule_id=15034055&alert_type=issue