Enable ingest attachment docs tests on JDK 11 (#34770)

These were disabled because ingest attachement was not playing well with
JDK 11. We have addressed that by upgrading the Tika dependency, yet
forgot to reenable these. This commit enables these tests again.

docs/build.gradle

@@ -61,17 +61,7 @@ integTestCluster {
   systemProperty 'es.scripting.update.ctx_in_params', 'false'
 }
 
-// remove when https://github.com/elastic/elasticsearch/issues/31305 is fixed
-if (rootProject.ext.compilerJavaVersion.isJava11()) {
-  integTestRunner {
-    systemProperty 'tests.rest.blacklist', [
-            'plugins/ingest-attachment/line_164',
-            'plugins/ingest-attachment/line_117'
-    ].join(',')
-  }
-}
-// Build the cluster with all plugins
-
+// build the cluster with all plugins
 project.rootProject.subprojects.findAll { it.parent.path == ':plugins' }.each { subproj ->
   /* Skip repositories. We just aren't going to be able to test them so it
    * doesn't make sense to waste time installing them. */