CI: pin isort version (pandas-dev#35136)

Author: AlexKirko

environment.yml

@@ -20,7 +20,7 @@ dependencies:
   - flake8<3.8.0  # temporary pin, GH#34150
   - flake8-comprehensions>=3.1.0  # used by flake8, linting of unnecessary comprehensions
   - flake8-rst>=0.6.0,<=0.7.0  # linting of code blocks in rst files
-  - isort  # check that imports are in the right order
+  - isort=4.3.21  # check that imports are in the right order
   - mypy=0.730
   - pycodestyle  # used by flake8
 

requirements-dev.txt

@@ -11,7 +11,7 @@ cpplint
 flake8<3.8.0
 flake8-comprehensions>=3.1.0
 flake8-rst>=0.6.0,<=0.7.0
-isort
+isort==4.3.21
 mypy==0.730
 pycodestyle
 gitpython