Update actions/cache version to 4.0 (#473)

According to GitHub guidelines

Author: hugtalbot

.github/workflows/ci.yml

@@ -40,7 +40,7 @@ jobs:
 
       - name: Setup cache for ccache files
         if: ${{ runner.os != 'Windows' }}
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: ${{ env.CCACHE_DIR }}
           key: ccache_${{ runner.os }}