Remove the text "Warning" from warning

[prakash-gds]

The gov uk design system doesn't show the text "Warning" in the Warning text, just the warning text icon and the actual text. This change makes the text "Warning" hidden to make it consistent with govuk design system

Referemce: https://design-system.service.gov.uk/components/warning-text/

[StuartMacKay]

Thanks for the pull request. The current version supports version 4.8.0 of the govuk design system. With the rapid updates to the 5.x versions since March 1st 2024 we'll need to think of how to track these changes better so it's easy to see which versions are compatible. Most likely the easiest path is simply to keep the same version numbers, so 5.3 of crispy-forms-gds is used with 5.3 of the govuk frontend. We'll merge in your pull request when we start that work (won't be long since we don't want to fall behind).