Add Pylint workflow for flake8. (#4571)

* remove

* Add pylint.
Co-authored-by: Steve <ubuntu@ip-172-31-34-29.ap-northeast-1.compute.internal>

.github/workflows/pylint.yml

+name: Pylint
+
+on: [push]
+
+jobs:
+  flake8_py3:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Setup Python
+        uses: actions/setup-python@v3
+        with:
+          python-version: 3.7.4
+          architecture: x64
+      - name: Checkout PyTorch
+        uses: actions/checkout@master
+      - name: Install flake8
+        run: pip install flake8
+      - name: Run flake8
+        uses: suo/flake8-github-action@releases/v1
+        # NOTE: this needs to be the same as the job name.
+        with:
+          checkName: 'flake8_py3'   
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}