fix(css): replace gl-sm-border-l-none with gl-md-border-l-solid
What does this MR do?
!2236 (merged) introduced the gl-sm-border-l-none utility which does not follow the responsive utility conventions as it relies on a max-width rather than min-width.
This replaces that utility with gl-md-border-l-solid, which does follow the conventions and should address what !2236 (merged) was meant to address.
How to consume this?
With the changes from !2236 (merged), you would remove left border style on small breakpoints by combining gl-border-l-solid with gl-sm-border-l-none.
With these changes, you would achieve the same style by combining gl-md-border-l-solid with gl-border-l-none.