fix(agents): compile shared runtime with Java 21

.github/workflows/agents-release.yml

@@ -76,9 +76,7 @@ jobs:
       - uses: actions/setup-java@v4
         with:
           distribution: temurin
-          java-version: |
-            8
-            21
+          java-version: "21"
       - uses: gradle/actions/setup-gradle@v4
       - run: ./gradlew shadowJar --parallel
         working-directory: agents