Return error when sensitive info fails to read body

As discovered in [this discussion](https://github.com/arcjet/arcjet-js/pull/5579#discussion_r2661978697) the sensitive info rule doesn't return an error when it fails to read the request body (at least for bun). It would be good to update our test-cases to differentiate between an error and an allow decision. See https://github.com/arcjet/arcjet-js/pull/5590 as an example. Per @wooorm-arcjet we'll also need to update node, deno, fastify (https://github.com/arcjet/arcjet-js/pull/5519). Right now this issue is phrased to return an error. Even if we decide that is not the correct thing to do the test change would still be helpful to enforce that decision.