Bump xarray from 0.20.2 to 0.21.1 in /extra_requirements (#908)

Bumps [xarray](https://github.com/pydata/xarray) from 0.20.2 to 0.21.1.
- [Release notes](https://github.com/pydata/xarray/releases)
- [Changelog](https://github.com/pydata/xarray/blob/main/HOW_TO_RELEASE.md)
- [Commits](pydata/xarray@v0.20.2...v0.21.1)

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

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

extra_requirements/requirements-tests.txt

@@ -39,5 +39,5 @@ tqdm==4.62.2
 typing_extensions==4.0.1                        # Tensorflow/bokeh dependency
 utilix==0.6.6
 wfsim==0.5.13; python_version<="3.9"            # nestpy doesn't work in py3.10
-xarray==0.20.2
+xarray==0.21.1
 zstd==1.5.1.0                                   # Strax dependency