Resolve "Lazy image loading breaks notification mails for an added screenshot"

What does this MR do?

It fixes the notification mail images as they were also rendered with lazy loading. I simply look now for the path variable set in the email filter.

Tested it by looking at generated output in development.log :

Why was this MR needed?

So images are visible again in notificaiton emails.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #37629 (closed)