Build against latest Paper API and local MobArena; fix CI JDK/artifact upload

.github/workflows/build.yml

@@ -19,13 +19,19 @@ jobs:
         uses: actions/setup-java@v4
         with:
           distribution: temurin
-          java-version: '11'
+          java-version: '25'
+
+      - name: Checkout MobArena
+        run: git clone --depth 1 https://git.tss3.us/skywalker3200/MobArena.git ../MobArena
+
+      - name: Publish MobArena to local Maven repo
+        run: cd ../MobArena && ./gradlew publishToMavenLocal --no-daemon
 
       - name: Build, test, package
         run: ./mvnw -B package --file pom.xml
 
       - name: Upload artifact
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v3
         with:
           name: MobArenaStats.jar
           path: target/MobArenaStats.jar