fix(per-tenant throttling): incorrect allowed_rps field in log message (#6869)

The `refill_interval` switched from a milliseconds usize to a Duration
during a review follow-up, hence this slipped through manual testing.

Part of https://github.com/neondatabase/neon/issues/5899

libs/pageserver_api/src/models.rs

@@ -340,7 +340,7 @@ impl ThrottleConfig {
     }
     /// The requests per second allowed  by the given config.
     pub fn steady_rps(&self) -> f64 {
-        (self.refill_amount.get() as f64) / (self.refill_interval.as_secs_f64()) / 1e3
+        (self.refill_amount.get() as f64) / (self.refill_interval.as_secs_f64())
     }
 }