ci: use JDK21 on GHA

.github/workflows/build.yml

@@ -12,7 +12,7 @@ jobs:
       matrix:
         # Use these Java versions
         java: [
-          17,    # Current Java LTS & minimum supported by Minecraft
+          21,
         ]
         # and run on both Linux and Windows
         os: [ubuntu-20.04, windows-2022, windows-2019, macos-12]
@@ -24,10 +24,11 @@ jobs:
       - name: validate gradle wrapper
         uses: gradle/wrapper-validation-action@v1
       - name: setup jdk ${{ matrix.java }}
-        uses: actions/setup-java@v1
+        uses: actions/setup-java@v4
         with:
+          distribution: 'zulu'
           java-version: ${{ matrix.java }}
-      - uses: actions/cache@v2
+      - uses: actions/cache@v4
         with:
           path: |
             ~/.gradle/caches
@@ -39,8 +40,8 @@ jobs:
       - name: build
         run: ./gradlew build
       - name: capture build artifacts
-        uses: actions/upload-artifact@v3
-        if: ${{ runner.os == 'Linux' && matrix.java == '17' }} # Only upload artifacts built from latest java on one OS
+        uses: actions/upload-artifact@v4
+        if: ${{ runner.os == 'Linux' && matrix.java == '21' }} # Only upload artifacts built from latest java on one OS
         with:
           name: artifacts
           path: |