Update cf-xarray requirement from <0.8.5,>=0.6.1 to >=0.6.1,<0.8.9

Updates the requirements on [cf-xarray](https://github.com/xarray-contrib/cf-xarray) to permit the latest version.
- [Release notes](https://github.com/xarray-contrib/cf-xarray/releases)
- [Commits](xarray-contrib/cf-xarray@v0.6.1...v0.8.8)

---
updated-dependencies:
- dependency-name: cf-xarray
  dependency-type: direct:production
...

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

pyproject.toml

@@ -34,7 +34,7 @@ dependencies = [
   "boltons>=20.1",
   "bottleneck>=1.3.1",
   # cf-xarray is differently named on conda-forge
-  "cf-xarray>=0.6.1,<0.8.5; python_version == '3.8'",
+  "cf-xarray>=0.6.1,<0.8.9; python_version == '3.8'",
   "cf-xarray>=0.6.1; python_version >= '3.9'",
   "cftime>=1.4.1",
   "Click>=8.1",