/usr/share/igtf-policy/classic/MARGI.namespaces is in igtf-policy-classic 1.88-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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#NAMESPACES-VERSION: 1.0
#
# @(#)$Id: 7d0d064a.namespaces,v 1.1 2008/03/14 08:34:26 pmacvsdg Exp $
# CA alias    : MARGI
#    subord_of: 
#    subjectDN: /C=MK/O=MARGI/CN=MARGI-CA
#    hash     : 7d0d064a
#    (generated automatically from 7d0d064a.signing_policy)
#
TO Issuer "/C=MK/O=MARGI/CN=MARGI-CA" \
  PERMIT Subject "/C=MK/O=MARGI/.*"
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