[Glitch] Use 1 column layout for form `ul` on narrow widths

Port 106b22bd2d to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/styles/forms.scss

@@ -313,6 +313,10 @@ code {
 
     ul {
       columns: 2;
+
+      @media screen and (max-width: $mobile-breakpoint) {
+        columns: 1;
+      }
     }
   }