[PostGIS] #5566: Add CI testing under sandboxed system

[PostGIS]

#5566: Add CI testing under sandboxed system
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  Reporter:  strk       |      Owner:  robe
      Type:  task       |     Status:  new
  Priority:  medium     |  Milestone:  Website Management, Bots
 Component:  buildbots  |    Version:
Resolution:             |   Keywords:  pgextwlist
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Comment (by strk):

 I've settled for a POSTGIS_REGRESS_ROLE_EXT_CREATOR environment variable
 support in run_test.pl which landed in the master branch with
 [52bfcd5faa3a7577292814d0a5a17c5698a9032f/git]

 In https://git.osgeo.org/gitea/postgis/postgis/pulls/158 I'm experimenting
 with that.
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Ticket URL: <https://trac.osgeo.org/postgis/ticket/5566#comment:4>
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