Revert "Increment version to 3.7.0-SNAPSHOT (#5291)" (#5295)

Author: Swiddis

build.gradle

@@ -6,7 +6,7 @@
 
 buildscript {
     ext {
-        opensearch_version = System.getProperty("opensearch.version", "3.7.0-SNAPSHOT")
+        opensearch_version = System.getProperty("opensearch.version", "3.6.0-SNAPSHOT")
         isSnapshot = "true" == System.getProperty("build.snapshot", "true")
         buildVersionQualifier = System.getProperty("build.version_qualifier", "")
         version_tokens = opensearch_version.tokenize('-')