add cache for workflow

.github/workflows/on_pull_request.yaml

@@ -22,6 +22,12 @@ jobs:
         uses: actions/setup-python@v3
         with:
           python-version: 3.10.6
+      - uses: actions/cache@v2
+        with:
+          path: ~/.cache/pip
+          key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}
+          restore-keys: |
+            ${{ runner.os }}-pip-
       - name: Install PyLint
         run: | 
           python -m pip install --upgrade pip