Increment version to 2.26.0 (opensearch-project#1595)

Signed-off-by: GitHub <[email protected]>
Co-authored-by: Xtansia <[email protected]>

Author: opensearch-trigger-bot[bot]

gradle.properties

@@ -1 +1 @@
-systemProp.version = 2.25.0
+systemProp.version = 2.26.0