Update pull_request.yml

bump py

.github/workflows/pull_request.yml

@@ -5,10 +5,10 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v1
-      - name: Setup python 3.6
+      - name: Setup python 3.8
         uses: actions/setup-python@v1
         with:
-          python-version: 3.6
+          python-version: 3.8
       - name: Install pre-commit
         run: pip install pre-commit
       - name: Run pre-commit