version bump from 6.8.3 to 6.8.4 (#46408)

Author: Paul Sanwald

.ci/bwcVersions

@@ -33,6 +33,7 @@ BWC_VERSION:
   - "6.8.1"
   - "6.8.2"
   - "6.8.3"
+  - "6.8.4"
   - "7.0.0"
   - "7.0.1"
   - "7.1.0"

server/src/main/java/org/elasticsearch/Version.java

@@ -108,6 +108,7 @@ public class Version implements Comparable<Version>, ToXContentFragment {
     public static final Version V_6_8_1 = new Version(6080199, org.apache.lucene.util.Version.LUCENE_7_7_0);
     public static final Version V_6_8_2 = new Version(6080299, org.apache.lucene.util.Version.LUCENE_7_7_0);
     public static final Version V_6_8_3 = new Version(6080399, org.apache.lucene.util.Version.LUCENE_7_7_0);
+    public static final Version V_6_8_4 = new Version(6080499, org.apache.lucene.util.Version.LUCENE_7_7_0);
     public static final Version V_7_0_0 = new Version(7000099, org.apache.lucene.util.Version.LUCENE_8_0_0);
     public static final Version V_7_0_1 = new Version(7000199, org.apache.lucene.util.Version.LUCENE_8_0_0);
     public static final Version V_7_1_0 = new Version(7010099, org.apache.lucene.util.Version.LUCENE_8_0_0);