Update CI: checkout@v4, setup-python@v5, drop pip cache

setup-python@v3 pip cache is returning 400 errors from GitHub's
cache service. Update to v4/v5 and remove pip caching to fix CI.

Author: iskandr

.github/workflows/tests.yml

@@ -19,12 +19,11 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v3
+        uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
-          cache: "pip"
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip