Merge branch 'docs-abuerer-clarify-secondary-runner' into 'master'

Update misleading automated tests note in Geo documentation

See merge request gitlab-org/gitlab!24883

doc/administration/geo/replication/index.md

@@ -30,7 +30,7 @@ Implementing Geo provides the following benefits:
 
 - Reduce from minutes to seconds the time taken for your distributed developers to clone and fetch large repositories and projects.
 - Enable all of your developers to contribute ideas and work in parallel, no matter where they are.
-- Balance the load between your **primary** and **secondary** nodes, or offload your automated tests to a **secondary** node.
+- Balance the read-only load between your **primary** and **secondary** nodes.
 
 In addition, it:
 
@@ -249,6 +249,7 @@ This list of limitations only reflects the latest version of GitLab. If you are
 - [Selective synchronization](configuration.md#selective-synchronization) applies only to files and repositories. Other datasets are replicated to the **secondary** node in full, making it inappropriate for use as an access control mechanism.
 - Object pools for forked project deduplication work only on the **primary** node, and are duplicated on the **secondary** node.
 - [External merge request diffs](../../merge_request_diffs.md) will not be replicated if they are on-disk, and viewing merge requests will fail. However, external MR diffs in object storage **are** supported. The default configuration (in-database) does work.
+- GitLab Runners cannot register with a **secondary** node. Support for this is [planned for the future](https://gitlab.com/gitlab-org/gitlab/issues/3294).
 
 ### Limitations on replication/verification