Doc: adjust examples of EXTRACT() output to match current reality.

Doc: adjust examples of EXTRACT() output to match current reality.

EXTRACT(EPOCH), EXTRACT(SECOND), and some related cases print more
trailing zeroes than they used to.  This behavior change happened
with commit a2da77cdb (Change return type of EXTRACT to numeric),
and it was intentional according to the commit log:

    - Return values when extracting fields with possibly fractional
      values, such as second and epoch, now have the full scale that the
      value has internally (so, for example, '1.000000' instead of just
      '1').

It's been like that for two releases now, so while I suggested
changing this back, it's probably better to adjust the documentation
examples.

Per bug #17866 from Евгений Жужнев.  Back-patch to v14 where the
change came in.

Discussion: https://postgr.es/m/17866-18eb70095b1594e2@postgresql.org