docs: Use 'az bicep upgrade' to ensure existing Bicep is bumped (Copilot review)

Author: Rafi-Microsoft

docs/AZD_DEPLOYMENT.md

@@ -36,8 +36,9 @@ This guide covers deploying the Content Generation Solution Accelerator using Az
 
 5. **Bicep CLI** v0.33.0 or higher (for compiling infrastructure templates)
    ```bash
-   # Install via Azure CLI
+   # Install or upgrade via Azure CLI (upgrade ensures an existing older Bicep is bumped to the required version)
    az bicep install
+   az bicep upgrade
 
    # Verify installation
    az bicep version