chore: update github actions to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -23,7 +23,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup java
         uses: actions/setup-java@v5
@@ -57,7 +57,7 @@ jobs:
         run: cp cloudnet-rest-module/build/libs/cloudnet-rest.jar cloudnet-rest.jar
 
       - name: Upload artifact jar
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: CloudNet-Rest
           path: cloudnet-rest.jar