Define index version 8500009 for use by 8.12.1 to enforce the CCR version boundary (#104754)

Bumps the index version used by 8.12.1 to enforce the CCR follower barrier between patch revisions. This version number was previously used by the first snapshot builds of 8.13, but 8.13 has since moved onto 8501000. This also does not conflict with serverless, as that uses version numbers unconnected with release versions - serverless and non-serverless do not talk to each other, so there is no possibility of a conflict with these numbers.

Author: thecoop

server/src/main/java/org/elasticsearch/index/IndexVersions.java

@@ -94,6 +94,7 @@ private static IndexVersion def(int id, Version luceneVersion) {
     public static final IndexVersion UPGRADE_LUCENE_9_9 = def(8_500_006, Version.LUCENE_9_9_0);
     public static final IndexVersion NORI_DUPLICATES = def(8_500_007, Version.LUCENE_9_9_0);
     public static final IndexVersion UPGRADE_LUCENE_9_9_1 = def(8_500_008, Version.LUCENE_9_9_1);
+    public static final IndexVersion ES_VERSION_8_12_1 = def(8_500_009, Version.LUCENE_9_9_1);
 
     /*
      * STOP! READ THIS FIRST! No, really,

x-pack/qa/rolling-upgrade-multi-cluster/src/test/java/org/elasticsearch/upgrades/CcrRollingUpgradeIT.java

@@ -206,7 +206,6 @@ public void testAutoFollowing() throws Exception {
         }
     }
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/104620")
     public void testCannotFollowLeaderInUpgradedCluster() throws Exception {
         if (upgradeState != UpgradeState.ALL) {
             return;