Change GlAlert variant for policy_editor_layout

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR resolves 396810

Follow up of this discussion

Changing Alert variant from info to warning

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

BEFORE	AFTER	AFTER

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Go to Security & Complience -> Policies -> New policy -> Scan Execution Policy (security/policies/new?type=scan_execution_policy)
2. Switch to yaml mode and type in invalid yaml key or non-existing tag-name, if you have no runner tags set up, any tag would be invalid

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #396810 (closed)