bump GWCS pin to `>=0.21.0,<0.23.0`

[zacharyburnett]

Checklist for PR authors (skip items if you don't have permissions or they are not applicable)

• [ ] added entry in CHANGES.rst within the relevant release section
• [ ] updated or added relevant tests
• [ ] updated relevant documentation
• [x] added relevant milestone
• [x] added relevant label(s)
• [ ] ran regression tests, post a link to the Jenkins job below. How to run regression tests on a PR
• [ ] All comments are resolved
• [ ] Make sure the JIRA ticket is resolved properly

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 59.54%. Comparing base (23fb5cd) to head (02af281). Report is 451 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #8598 +/- ## ======================================= Coverage 59.54% 59.54% ======================================= Files 391 391 Lines 39292 39292 ======================================= Hits 23396 23396 Misses 15896 15896 ```

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