[ Reason ]
A new upstream version of tzdata, 2026c, has been released with a change
for Alberta which moved to permanent -06 since 2026-06-18 and for
Morroco which will move to permanent +00 on 2026-09-20.

[ Impact ]
If this version is not accepted, the clock of users in Morroco will
start differing on 2026-09-20 and the clock of users in Alberta will
start differing on 2026-11-01. Therefore it is important to get this in
the 13.7 release.

[ Tests ]
There are no tests for this change.

[ Risks ]
The risk to import new upstream versions of tzdata are quite low, and is
done routinely. This upstream version is already in testing and sid for
more than a month.

[ 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 (old)stable
  [x] the issue is verified as fixed in unstable

[ Changes ]
The 2026c upstream version contains the following changes to
past and future timestamps:
- Alberta moved to permanent -06 on 2026-06-18, so it will not fall back
  from -06 to -07 on 2026-11-01.
- Morocco moves to permanent +00 on 2026-09-20.

It also updates the leapseconds file with a new expiration date to
2027-06-28.

[ Other info ]
Given the changes are relatively small, I have just uploaded the package.