docs: make tags restrictions a subsection in worker groups (#1032)

Convert the tags restriction content to a proper subsection within 
the "Set tags to assign specific queues" section for better 
documentation organization.

Fixes #1031

Co-authored-by: claude[bot] <209825114+claude[bot]@users.noreply.github.com>
Co-authored-by: Ruben Fiszel <[email protected]>

Author: claude[bot]

docs/core_concepts/9_worker_groups/index.mdx

@@ -167,6 +167,8 @@ To make custom tags available from the UI, go to the dedicated "Workers" tab on
 
 ![Worker Group Assignable Tags](./worker_group_ui_2.png.webp)
 
+#### Restrict tags to specific workspaces
+
 It is possible to restrict some tags to specific workspace using the following syntax:
 
 ```