chore(deps): update bellsoft/liberica-openjdk-alpine docker tag to v21 (#9530)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

benchmark-overhead/Dockerfile-petclinic-base

@@ -13,7 +13,7 @@ RUN git checkout 8aa4d49
 RUN ./mvnw package -Dmaven.test.skip=true
 RUN cp target/spring-petclinic-rest*.jar /app/spring-petclinic-rest.jar
 
-FROM bellsoft/liberica-openjdk-alpine:20
+FROM bellsoft/liberica-openjdk-alpine:21
 COPY --from=app-build /app/spring-petclinic-rest.jar /app/spring-petclinic-rest.jar
 WORKDIR /app
 EXPOSE 9966