unpin pip 20.2 again (#4656)

* unpin pip 20.2 again

* [test-upstream] trigger upstream-dev

* [test-upstream] trigger upstream-dev

* [test-upstream] [skip-ci]

Co-authored-by: Keewis <[email protected]>

Author: mathause

ci/requirements/environment.yml

@@ -26,7 +26,7 @@ dependencies:
   - numpy
   - pandas
   - pint
-  - pip=20.2
+  - pip
   - pooch
   - pre-commit
   - pseudonetcdf