disable annotation processor for docs

Could not find evidence that the log4j annotation processor is used.
The compiler flag enables the Gradle 5.0 behavior

Closes #30476

Author: alpar-t

docs/build.gradle

@@ -226,6 +226,12 @@ buildRestTests.doFirst {
     buildRestTests.setups['bank'].replace('#bank_data#', accounts)
 }
 
+compileTestJava {
+  // compile classpath leaks org.apache.logging.log4j.core.config.plugins.processor.PluginProcessor but we don't need
+  // annotation processors here. This will be the default in Gradle 5.0
+  options.compilerArgs += '-proc:none'
+}
+
 buildRestTests.setups['range_index'] = '''
   - do :
         indices.create: