CI: (deps): Bump traitlets from 5.14.3 to 5.15.0 in /ci

Bumps [traitlets](https://github.com/ipython/traitlets) from 5.14.3 to 5.15.0.
- [Release notes](https://github.com/ipython/traitlets/releases)
- [Changelog](https://github.com/ipython/traitlets/blob/main/CHANGELOG.md)
- [Commits](ipython/traitlets@v5.14.3...v5.15.0)

---
updated-dependencies:
- dependency-name: traitlets
  dependency-version: 5.15.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

ci/requirements.txt

@@ -5,5 +5,5 @@ pooch==1.9.0
 pint==0.25.3
 pyproj==3.7.2
 scipy==1.17.1
-traitlets==5.14.3
+traitlets==5.15.0
 xarray==2025.10.1