bump bwc to 2.6.0

We need to bump the version because only the latest 2.x will be upgradable to 3.0 when that ship. Since OpenSearch core bumped to 2.6, we need to do that as well. Note after bumping version, bwc still fails to find 2.6.0 core zip.

Signed-off-by: Kaituo Li <kaituo@amazon.com>

build.gradle

@@ -34,7 +34,7 @@ buildscript {
         js_resource_folder = "src/test/resources/job-scheduler"
         common_utils_version = System.getProperty("common_utils.version", opensearch_build)
         job_scheduler_version = System.getProperty("job_scheduler.version", opensearch_build)
-        bwcVersionShort = "2.5.0"
+        bwcVersionShort = "2.6.0"
         bwcVersion = bwcVersionShort + ".0"
         bwcOpenSearchADDownload = 'https://ci.opensearch.org/ci/dbc/distribution-build-opensearch/' + bwcVersionShort + '/latest/linux/x64/tar/builds/' +
                 'opensearch/plugins/opensearch-anomaly-detection-' + bwcVersion + '.zip'