Rephrase comment in OldCodecsAvailableTests

This isn't a blocker for the lucene 10 upgrade, it is for the release of stack 9.
It's already annotated @UpdateForV9 so we are good.

Author: javanna

x-pack/plugin/old-lucene-versions/src/test/java/org/elasticsearch/xpack/lucene/bwc/codecs/OldCodecsAvailableTests.java

@@ -18,7 +18,7 @@ public class OldCodecsAvailableTests extends ESTestCase {
      * to the next major Lucene version.
      */
     @UpdateForV9
-    @AwaitsFix(bugUrl = "muted until we add bwc codecs as part of lucene 10 upgrade")
+    @AwaitsFix(bugUrl = "muted until we add bwc codecs to support 7.x indices in Elasticsearch 9.0")
     public void testLuceneBWCCodecsAvailable() {
         assertEquals("Add Lucene BWC codecs for Elasticsearch version 7", 8, Version.CURRENT.major);
     }