Bump to unreleased version 6.2.4 (#29171)

Author: Christoph Büscher

buildSrc/version.properties

@@ -1,4 +1,4 @@
-elasticsearch     = 6.2.3
+elasticsearch     = 6.2.4
 lucene            = 7.2.1
 
 # optional dependencies

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

@@ -158,7 +158,9 @@ public class Version implements Comparable<Version> {
     public static final Version V_6_2_2 = new Version(V_6_2_2_ID, org.apache.lucene.util.Version.LUCENE_7_2_1);
     public static final int V_6_2_3_ID = 6020399;
     public static final Version V_6_2_3 = new Version(V_6_2_3_ID, org.apache.lucene.util.Version.LUCENE_7_2_1);
-    public static final Version CURRENT = V_6_2_3;
+    public static final int V_6_2_4_ID = 6020499;
+    public static final Version V_6_2_4 = new Version(V_6_2_4_ID, org.apache.lucene.util.Version.LUCENE_7_2_1);
+    public static final Version CURRENT = V_6_2_4;
 
     static {
         assert CURRENT.luceneVersion.equals(org.apache.lucene.util.Version.LATEST) : "Version must be upgraded to ["
@@ -171,6 +173,8 @@ public static Version readVersion(StreamInput in) throws IOException {
 
     public static Version fromId(int id) {
         switch (id) {
+            case V_6_2_4_ID:
+                return V_6_2_4;
             case V_6_2_3_ID:
               return V_6_2_3;
             case V_6_2_2_ID: