Increase timeout in statement_timeout test from 1 second to 2 seconds.

We have once or twice seen failures suggesting that control didn't get
to the exception block before the timeout elapsed, which is unlikely
but not impossible in a parallel regression test (with a dozen other
backends competing for cycles).  This change doesn't completely prevent
the problem of course, but it should reduce the probability enough that
we don't see it anymore.  Per buildfarm results.