update GHA actions version to avoid node.js warnings

.github/workflows/python-package.yml

@@ -37,7 +37,7 @@ jobs:
     # manually if/when you want to upgrade Poetry, or if something goes wrong. This could be
     # mildly cleaner by using an environment variable, but I don't really care.
     - name: cache poetry install
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ~/.local
         key: poetry-1.1.12-0
@@ -62,7 +62,7 @@ jobs:
     # them in the cache key. I'm not, so it can be simple and just depend on the poetry.lock.
     - name: cache deps
       id: cache-deps
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: .venv
         key: pydeps-${{ hashFiles('**/poetry.lock') }}