fix: resolve Premium license text rendering issue

Replace inline markdown link with separate text and link to prevent
rendering engines from concatenating 'a' with '[Premium]' into 'aPremium'.

Fixes the display issue where 'External agents require aPremium Coder license'
was shown instead of 'External agents require a Premium Coder license'.

Co-authored-by: Matt Vollmer <[email protected]>

Author: blink-so[bot]

registry/coder-labs/templates/externally-managed-workspace/README.md

@@ -9,7 +9,7 @@ tags: [external]
 # Externally Managed Workspace Template
 
 > [!IMPORTANT]
-> External agents require a [Premium](https://coder.com/pricing) Coder license.
+> External agents require a Premium Coder license. [Learn more](https://coder.com/pricing).
 
 This template provides a minimal scaffolding for creating Coder workspaces that connect to externally provisioned compute resources.