Bump org.opensearch:opensearch-core

Bumps [org.opensearch:opensearch-core](https://github.com/opensearch-project/OpenSearch) from current to 2.6.0.
- [Release notes](https://github.com/opensearch-project/OpenSearch/releases)
- [Changelog](https://github.com/opensearch-project/OpenSearch/blob/main/CHANGELOG.md)
- [Commits](https://github.com/opensearch-project/OpenSearch/commits/2.6.0)

---
updated-dependencies:
- dependency-name: org.opensearch:opensearch-core
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

buildSrc/src/testKit/opensearch.build/build.gradle

@@ -21,7 +21,7 @@ dependencies {
   api "junit:junit:${versions.junit}"
   // missing classes in thirdparty audit
   api 'org.hamcrest:hamcrest-core:1.3'
-  jdkJarHell 'org.opensearch:opensearch-core:current'
+  jdkJarHell 'org.opensearch:opensearch-core:2.6.0'
 }
 
 repositories {