Update cache action to v4

Author: osirisinferi

.github/workflows/ci.yml

@@ -34,7 +34,7 @@ jobs:
         uses: actions/checkout@v3
 
       - name: Cache portage binary packages
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         env:
           cache-name: cache-binpgks
         with:
@@ -43,7 +43,7 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-${{ env.cache-name }}-${{ secrets.CACHE_VERSION }}-
       - name: Cache portage distfiles
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         env:
           cache-name: cache-distfiles
         with: