chore: update xarray requirement (#669)

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@v2024.02.0...v2026.04.0)

---
updated-dependencies:
- dependency-name: xarray
  dependency-version: 2026.4.0
  dependency-type: direct:production
...

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pyproject.toml

@@ -34,7 +34,7 @@ dependencies = [
     # Core scientific computing
     "numpy >= 1.21.5, < 3",
     "pandas >= 2.0.0, < 3",
-    "xarray >=2024.2.0, <2026.3", # CalVer: allow through next calendar year
+    "xarray >=2024.2.0, <2026.5", # CalVer: allow through next calendar year
     # Optimization and data handling
     "linopy >=0.5.1, <0.7", # Widened from patch pin to minor range
     "netcdf4 >=1.6.1, <1.7.5",  # 1.7.4 missing wheels, revert to < 2 later