upgrade actions/cache to v4

Author: mrlevitas

.github/workflows/python-package.yaml

@@ -23,7 +23,7 @@ jobs:
       with:
         python-version: ${{ matrix.python-version }}
 
-    - uses: actions/cache@v2
+    - uses: actions/cache@v4
       with:
         path: ~/.cache/pip
         key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements*.txt') }}