FIx testReplicaIgnoresOlderRetentionLeasesVersion (elastic#38246)

If the innerLength is 0, the version won't be increased; then there will
be two RetentionLeases with the same term and version, but their leases
are different.

Relates elastic#37951
Closes elastic#38245

server/src/test/java/org/elasticsearch/index/seqno/ReplicationTrackerRetentionLeaseTests.java

@@ -339,8 +339,8 @@ public void testReplicaIgnoresOlderRetentionLeasesVersion() {
             for (int j = 0; j < innerLength; j++) {
                 leases.add(
                         new RetentionLease(i + "-" + j, randomNonNegativeLong(), randomNonNegativeLong(), randomAlphaOfLength(8)));
-                version++;
             }
+            version++;
             if (rarely()) {
                 primaryTerm++;
             }