ci: skip javadoc for the benchmark module

The benchmark pom already documented exemption from the javadoc gate but only
set maven.deploy.skip; JMH-generated sources were tripping failOnWarnings and
failing CI's full-reactor verify. Add the intended maven.javadoc.skip.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: dfa1

benchmark/pom.xml

@@ -23,6 +23,7 @@
 		<zstd-jni.version>1.5.7-11</zstd-jni.version>
 		<aircompressor.version>3.6</aircompressor.version>
 		<!-- Benchmark code is exempt from the Javadoc gate; checkstyle still applies. -->
+		<maven.javadoc.skip>true</maven.javadoc.skip>
 		<maven.deploy.skip>true</maven.deploy.skip>
 	</properties>