Pin isort to restore the lint step in CI

[krassowski]

References

#290 shows a failure in the lint step (all the actual tests pass ok). The root cause seems to be a recent release of isort (5.0) which affects nblint and pylint. Until both have migrated to isort 5.0 the proposed solution is to pin isort <5.

Upstream/root issues:

• Support both isort 4 and isort 5 pylint-dev/pylint#3725
• Upgrade nblint.py to work with isort 5.0 #292 for our nblint.py script

 robot --name Linux37 --outputdir /home/vsts/work/1/s/atest/output/dry_run_linux_37_1 --output /home/vsts/work/1/s/atest/output/dry_run_linux_37_1.robot.xml --log /home/vsts/work/1/s/atest/output/dry_run_linux_37_1.log.html --report /home/vsts/work/1/s/atest/output/dry_run_linux_37_1.report.html --xunitskipnoncritical --xunit /home/vsts/work/1/s/atest/output/dry_run_linux_37_1.xunit.xml --variable OS:Linux --variable PY:37 --randomize all --dryrun --console quiet --noncritical language:yamlANDfeature:config --noncritical language:pythonANDpy:36ANDos:windows /home/vsts/work/1/s/atest
0 errors in 2 seconds
..Traceback (most recent call last):
  File "scripts/nblint.py", line 87, in <module>
    sys.exit(nblint())
  File "scripts/nblint.py", line 64, in nblint
    new = isort.SortImports(file_contents=source).output
AttributeError: module 'isort' has no attribute 'SortImports'

Code changes

Pin isort in:

• binder/environment.yml
• requirements/lint.yml

User-facing changes

None

Backwards-incompatible changes

None

Chores

• linted
• tested
• documented
• changelog entry

[bollwyvl]

🎉

[bollwyvl]

👍 have had to do this in some other places.