Move the strings, numerology, insert, insert_conflict, select and
errors tests to be parts of nearby parallel groups, instead of
executing by themselves.  (Moving "select" required adjusting the
constraints test, which uses a table named "tmp" as select also
does.  There don't seem to be any other conflicts.)

Move psql and stats_ext to the next parallel group, where the rules
test also has a long runtime.  To make it safe to run stats_ext in
parallel with rules, I adjusted the latter to only dump views/rules
from the pg_catalog and public schemas, which was what it was doing
anyway.  stats_ext makes some views in a transient schema, which now
will not affect rules.

Reorder serial_schedule to match parallel_schedule.

Discussion: https://postgr.es/m/735.1554935715@sss.pgh.pa.us