Upgrade deprecated cache plugin

Author: WhyNotHugo

.github/workflows/test.yml

@@ -32,7 +32,7 @@ jobs:
         echo "::set-output name=dir::$(pip cache dir)"
 
     - name: Cache
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ${{ steps.pip-cache.outputs.dir }}
         key: