[PostGIS] #5950: Document the use of POSTGIS_REGRESS_DB_OWNER

[PostGIS]

#5950: Document the use of POSTGIS_REGRESS_DB_OWNER
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  Reporter:  robe           |      Owner:  robe
      Type:  defect         |     Status:  new
  Priority:  medium         |  Milestone:  PostGIS 3.6.0
 Component:  documentation  |    Version:  3.5.x
Resolution:                 |   Keywords:
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Comment (by strk):

 The variable is documented in output of `regress/run_test.pl` when called
 without arguments, togheter with POSTGIS_REGRESS_ROLE_EXT_CREATOR

 It still takes superuser to tweak the `lc_messages` setting, the variable
 is only needed to TEST unprivileged user creating and using postgis WHEN
 the database allows to do so to unprivileged users.. (it takes a
 PostgreSQL module to allow that).

 Allowing non-superusers accounts to create the PostGIS extension would
 require a change on our side to mark the extension as trusted, as
 requested by #5567 (which was closed as a won't fix)
-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/5950#comment:1>
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