[PostGIS] #5532: Improve validation of PostGIS Manual docbook

[PostGIS]

#5532: Improve validation of PostGIS Manual docbook
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  Reporter:  strk           |      Owner:  strk
      Type:  defect         |     Status:  assigned
  Priority:  medium         |  Milestone:  PostGIS 3.7.0
 Component:  documentation  |    Version:  master
Resolution:                 |   Keywords:
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Comment (by Darafei Praliaskouski <me@…>):

 In [changeset:"650756cd29999db62384b98f1c2e876c6a61efc6/git" 650756c/git]:
 {{{#!CommitTicketReference repository="git"
 revision="650756cd29999db62384b98f1c2e876c6a61efc6"
 doc: validate manual with DocBook XMLSchema

 Detect the DocBook 5 XMLSchema during configure and include XMLSchema
 validation in the documentation check target.

 References #5532

 Closes https://github.com/postgis/postgis/pull/967
 }}}
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Ticket URL: <https://trac.osgeo.org/postgis/ticket/5532#comment:7>
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