Try caching pip packages

.github/workflows/pytest.yml

@@ -14,15 +14,24 @@ jobs:
         python-version: ["3.9"]
     steps:
     - uses: actions/checkout@v3
+
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v3
       with:
         python-version: ${{ matrix.python-version }}
 
+    - name: Cache pip packages
+      uses: actions/cache@v3
+      with:
+        path: ~/.cache/pip
+        key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}
+        restore-keys: |
+          ${{ runner.os }}-pip-
+
     - name: Install dependencies
       run: |
-        pip install wheel setuptools pip --upgrade
-        pip install flake8 pytest pytest-xdist-forked
+        pip install --upgrade pip setuptools wheel
+        pip install -r requirements.txt
         pip install .
 
     - name: Lint with flake8