Chore(deps-dev): Update xarray requirement from <2025 to <2026

Updates the requirements on [xarray](https://github.com/pydata/xarray) to permit the latest version.
- [Release notes](https://github.com/pydata/xarray/releases)
- [Commits](pydata/xarray@v0.1...v2025.12.0)

---
updated-dependencies:
- dependency-name: xarray
  dependency-version: 2025.12.0
  dependency-type: direct:development
...

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

Author: dependabot[bot]

pyproject.toml

@@ -131,7 +131,7 @@ optional-dependencies.scientific = [
   "cfgrib<1",
   "cftime<2",
   "scipy<2",
-  "xarray<2025",
+  "xarray<2026",
 ]
 optional-dependencies.test = [
   "pytest<9",