Bump scipp from 25.11.0 to 25.12.0 in /requirements

Bumps [scipp](https://github.com/scipp/scipp) from 25.11.0 to 25.12.0.
- [Release notes](https://github.com/scipp/scipp/releases)
- [Commits](scipp/scipp@25.11.0...25.12.0)

---
updated-dependencies:
- dependency-name: scipp
  dependency-version: 25.12.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements/base.txt

@@ -67,7 +67,7 @@ python-dateutil==2.9.0.post0
     #   scippneutron
 sciline==25.11.1
     # via -r base.in
-scipp==25.11.0
+scipp==25.12.0
     # via
     #   -r base.in
     #   scippneutron

requirements/basetest.txt

@@ -99,7 +99,7 @@ python-dateutil==2.9.0.post0
     # via matplotlib
 requests==2.32.5
     # via pooch
-scipp==25.11.0
+scipp==25.12.0
     # via tof
 scipy==1.16.3
     # via -r basetest.in