Update to current version of actions/cache (v5)

Author: mgedmin

.github/workflows/build.yml

@@ -87,7 +87,7 @@ jobs:
           python-version: "${{ env.default_python || '3.12' }}"
 
       - name: Pip cache
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: ~/.cache/pip
           key: ${{ runner.os }}-pip-${{ matrix.toxenv }}-${{ hashFiles('tox.ini') }}