[ Reason ]
I would like to update the gnustep-base package in trixie to fix
#1150228 (severity: important).  It was reported by one of the sogo
maintainers, it is fixed in unstable/testing and affects also stable.

[ Impact ]
There are at least two UI regressions in sogo/5.12.1-3+deb13u3
(DSA-6561-1) due to this bug and they will remain unfixed.  They are
descibed at #1150228.

[ Tests ]
The upstream change includes test cases.  The NSRegularExpression
class is seldom used so I rely on them and on runtime tests performed
by sogo maintainers/users.

[ Risks ]
The change is pretty straightforward and I would classify it as low risk.

[ Checklist ]
  [X] *all* changes are documented in the d/changelog
  [X] I reviewed all changes and I approve them
  [X] attach debdiff against the package in stable
  [X] the issue is verified as fixed in unstable