Increment version to 2.19.4-SNAPSHOT (#764)

Signed-off-by: opensearch-ci-bot <opensearch-infra@amazon.com>
Co-authored-by: opensearch-ci-bot <opensearch-infra@amazon.com>

Author: opensearch-trigger-bot[bot]

build.gradle

@@ -10,7 +10,7 @@ buildscript {
         distribution = 'oss-zip'
         opensearch_group = "org.opensearch"
         isSnapshot = "true" == System.getProperty("build.snapshot", "true")
-        opensearch_version = System.getProperty("opensearch.version", "2.19.3-SNAPSHOT")
+        opensearch_version = System.getProperty("opensearch.version", "2.19.4-SNAPSHOT")
         opensearch_plugin_version = System.getProperty("bwc.version", "2.10.0.0")
         buildVersionQualifier = System.getProperty("build.version_qualifier", "")
         // 2.0.0-rc1-SNAPSHOT -> 2.0.0.0-rc1-SNAPSHOT