pybind/mgr/pg_autoscaler: fix warn when not too few pgs

pybind/mgr/pg_autoscaler: fix warn when not too few pgs

Problem:

when `pg_num_final` is equal to `pg_num_target`
we get too many PGs warnings in ceph health while
`warn` mode in the autoscaler.

Solution:

Get rid of `else` condition and add an
`elif p['pg_num_final'] < p['pg_num_target']`
instead

Fixes: https://tracker.ceph.com/issues/61570
Signed-off-by: Kamoltat <ksirivad@redhat.com>
(cherry picked from commit bfef56701f576d1a62017d313839a0c36949ac00)