server-test-host: Rethrown exception in StatusPages exception handler fails test

**Ktor Version and Engine Used (client or server and name)**
Using ktor server 1.3.1, with `ktor-server-test-host`

**Describe the bug**
When using the `StatusPages` feature to handle exceptions, a rethrowing the exception will bubble out to the test and cause a failure even if it was successfully handled with a `call.respond`. Rethrowing exceptions is suggested as a way to log caught exceptions in the documentation: https://ktor.io/servers/features/status-pages.html#logging-exceptions

**To Reproduce**
```kotlin
@Test
fun test() {
open class MyException : RuntimeException()

withTestApplication({
install(StatusPages) {
exception {
call.respond(HttpStatusCode.UnprocessableEntity, it.toString())
throw it // Comment out this line to pass test, but not log exception
}
}
routing {
get("/") {
throw MyException()
}
}
}) {
with(handleRequest {
method = HttpMethod.Get
uri = "/"
}) {
assertEquals(HttpStatusCode.UnprocessableEntity, response.status())
}
}
}
```

**Expected behavior**
I expect the above test to pass, and the exception to be logged as it would in a non-test application

Start by running the provided withTestApplication and handleRequest reproduction with ktor-server-test-host, then inspect the StatusPages exception path used by the test host. Compare behavior when the exception is rethrown versus omitted; done means the response remains UnprocessableEntity, the test does not fail, and the exception can still be logged.

Written by the indexing model from the issue text.