Fix template _msearch with extra tokens

This change removes the check for extra tokens when parsing a source generated by a templated
_msearch request. This was added unintentionally in elastic#29428 but the intent of this modification was to validate
simple _search request only.

Author: jimczi

modules/lang-mustache/src/main/java/org/elasticsearch/script/mustache/TransportSearchTemplateAction.java

@@ -112,7 +112,7 @@ static SearchRequest convert(SearchTemplateRequest searchTemplateRequest, Search
         try (XContentParser parser = XContentFactory.xContent(XContentType.JSON)
                 .createParser(xContentRegistry, LoggingDeprecationHandler.INSTANCE, source)) {
             SearchSourceBuilder builder = SearchSourceBuilder.searchSource();
-            builder.parseXContent(parser, true);
+            builder.parseXContent(parser, false);
             builder.explain(searchTemplateRequest.isExplain());
             builder.profile(searchTemplateRequest.isProfile());
             searchRequest.source(builder);