Update release version for full text search

Per the PM in issue 202121, full text searching was rolled out without
an announcement in 12.7, but is being announced as part of 12.8.
This commit updates the release version listed as part of the
feature.

doc/user/project/clusters/kubernetes_pod_logs.md

@@ -57,7 +57,7 @@ Support for historical data is coming [in a future release](https://gitlab.com/g
 
 ### Full text search
 
-> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/21656) in GitLab 12.7.
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/21656) in GitLab 12.8.
 
 When you enable [Elastic Stack](../../clusters/applications.md#elastic-stack) on your cluster,
 you can search the content of your logs via a search bar.