Bump actions/upload-artifact from 5 to 6 (#4)

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/gradle.yml

@@ -22,7 +22,7 @@ jobs:
       - name: Build with Gradle
         run: ./gradlew buildAndCollect
       - name: Upload artifact
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: "Topper"
           path: "build/libs/*/topper*.jar"