fix(form): adjust error prompt display in grouped inline fields

When error prompts appear on checkboxes inside of grouped inline fields, there was no distance between error prompts in comparison to single inline fields.
This PR slightly adjusts the bottom margin , so the distance looks better (not exactly equal to single inline fields, because the grouping should still be recognizable)

Author: lubber-de

src/definitions/collections/form.less

@@ -860,6 +860,9 @@
     margin: @groupedFieldMargin;
     padding: 0;
   }
+  .ui.form .grouped.inline.fields .ui.checkbox {
+    margin-bottom: @groupedInlineCheckboxBottomMargin;
+  }
 }
 
 /*--------------------

src/themes/default/collections/form.variables

@@ -161,6 +161,7 @@
 @inlineCalendarWidth: 13.11em;
 
 @groupedInlineLabelMargin: 0.035714em 1em 0 0;
+@groupedInlineCheckboxBottomMargin: 0.4em;
 
 /*-------------------
        Groups