Resolve "Upgrade xarray dependency to 0.16"

This MR bumps the xarray dependency to 0.16.0

Can this MR be accepted?

• Implementation ready
• Tests added or adjusted
• Documentation extended or updated

• Code quality
  • Changes follow coding guidelines
  • Checked code coverage on new and adjusted code ...
    • … losing two lines that were previously covered but can only be reached with xarray < 0.16. Leaving them in, though.

• Ready for merging
  • Pipeline passes without warnings
  • Squash option set
  • Changelog entry added
  • Version number bumped
  • Minor change, not asking for review

Related issues

Closes #195 (closed)