Revert Hibernate version to 6.2.6.Final

It looks like in the latest Hibernate there is some fix
in the persistent context where provided entity is updated by the values from
DB.

We are going to address those failing JPA tests post-release

Author: artembilan

build.gradle

@@ -67,7 +67,7 @@ ext {
     groovyVersion = '4.0.15'
     hamcrestVersion = '2.2'
     hazelcastVersion = '5.2.4'
-    hibernateVersion = '6.2.8.Final'
+    hibernateVersion = '6.2.6.Final'
     hsqldbVersion = '2.7.2'
     h2Version = '2.2.224'
     jacksonVersion = '2.15.2'