Align versions of hippo-essentials and hippo-testsuite to the product release version

Since v13.0 the version of the projects based on the release pom use the same major/minor/patch version as the release. To align project layout across releases update the project version of the hippo-testsuite and hippo-essentials projects to use the same versions, so 11.2.x and 12.6.x. As the artifacts of these projects are for local usage and not intended to be in a distribution this should not have any impact on product environments.