use isort==4.3.21 since >= 5.x.x produces different import sorting compared to platform009's isort

Summary:
`isort==5.8.0` produces different sorting order compared to platform009's `isort` (not sure which version is used with platform009 but `isort==4.3.21` is the one we used to use for `pytorch/elastic` which produces consistent results to our internal `arc f`.

This should fix linter failures for both:
1. pytorch#12
2. pytorch#10

Reviewed By: d4l3k

Differential Revision: D28669450

fbshipit-source-id: 8ead84f96d2ef2d0c01ddaba2ce513c78f7966f3

Author: Kiuk Chung

.github/workflows/lint.yaml

@@ -20,7 +20,7 @@ jobs:
       - name: Install Dependencies
         run: |
           set -eux
-          pip install isort
+          pip install isort==4.3.21
           pip install black
       - name: Run Lint
         run: |

dev-requirements.txt

@@ -3,7 +3,7 @@ moto>=2.0.6
 kfp==1.4.0
 pyre-extensions>=0.0.21
 black>=21.5b1
-isort>=5.8.0
+isort==4.3.21
 pytorch-lightning>=0.5.3
 torch>=1.8.1
 torchvision>=0.9.1