feat(ci): cache pip requirements

Author: crccheck

.github/workflows/ci.yml

@@ -36,6 +36,13 @@ jobs:
       - uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
+      - name: Cache pip
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/pip
+          key: ${{ runner.os }}-pip-${{ matrix.python-version }}-${{ matrix.django-version }}
+          restore-keys: |
+            ${{ runner.os }}-pip-
       - run: pip install -e '.[dev]'
       - run: pip install "Django==${{ matrix.django-version }}.*"
       - run: make test