Update CI to include JDK 21, dependabot updates for actions

.github/dependabot.yml

@@ -0,0 +1,10 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    groups:
+      github-actions:
+        patterns:
+          - "*"

.github/workflows/main.yml

@@ -22,14 +22,14 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        java_version: ['8', '11', '17']
+        java_version: ['8', '11', '17', '21']
         os: ['ubuntu-20.04']
     env:
       JAVA_OPTS: "-XX:+TieredCompilation -XX:TieredStopAtLevel=1"
     steps:
-    - uses: actions/[email protected].0
+    - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
     - name: Set up JDK
-      uses: actions/setup-java@v3
+      uses: actions/setup-java@387ac29b308b003ca37ba93a6cab5eb57c8f5f93 # v4.0.0
       with:
         distribution: 'temurin'
         java-version: ${{ matrix.java_version }}
@@ -57,7 +57,7 @@ jobs:
       run: ./mvnw -B -q -ff -ntp test
     - name: Publish code coverage
       if: github.event_name != 'pull_request' && matrix.java_version == '8'
-      uses: codecov/codecov-action@v1
+      uses: codecov/codecov-action@e0b68c6749509c5f83f984dd99a76a1c1a231044 # v4.0.1
       with:
         token: ${{ secrets.CODECOV_TOKEN }}
         file: ./target/site/jacoco/jacoco.xml