Commit 4318daec introduced a test that
couldn't be made consistent between integer and floating-point
timestamps.

It was designed to test the longest possible interval output length,
so removing four zeros from the number of hours, as this patch does,
is not ideal. But the test still has some utility for its original
purpose, and there aren't a lot of other good options.

Noah Misch suggested a different approach where we test that the
output either matches what we expect from integer timestamps or what
we expect from floating-point timestamps. That seemed to obscure an
otherwise simple test, however.

Reviewed by Tom Lane and Noah Misch.