Fix inappropriate reference to RRFRankPlugin.NAME

Author: Mikep86

x-pack/plugin/rank-rrf/src/test/java/org/elasticsearch/xpack/rank/rrf/RRFRetrieverBuilderTests.java

@@ -145,15 +145,15 @@ protected NamedXContentRegistry xContentRegistry() {
         entries.add(
             new NamedXContentRegistry.Entry(
                 RetrieverBuilder.class,
-                new ParseField(RRFRankPlugin.NAME),
+                new ParseField(RRFRetrieverBuilder.NAME),
                 (p, c) -> RRFRetrieverBuilder.fromXContent(p, (RetrieverParserContext) c)
             )
         );
         // Add an entry with no license requirement for unit testing
         entries.add(
             new NamedXContentRegistry.Entry(
                 RetrieverBuilder.class,
-                new ParseField(RRFRankPlugin.NAME + "_nl"),
+                new ParseField(RRFRetrieverBuilder.NAME + "_nl"),
                 (p, c) -> RRFRetrieverBuilder.PARSER.apply(p, (RetrieverParserContext) c)
             )
         );