Fixes affix-top class not applying

Use scrollTop instead of colliderTop which uses the elements
offset().top, as the offset top does not account for padding.

This issue can be replicated by using a navbar-fixed-top and applying
relevant padding to the body. (A navbar-static-top with no padding on
the body does not encounter this issue)

Fixes #15078
Closes #15154 by merging it

js/affix.js

@@ -53,7 +53,7 @@
     var colliderTop    = initializing ? scrollTop : position.top
     var colliderHeight = initializing ? targetHeight : height
 
-    if (offsetTop != null && colliderTop <= offsetTop) return 'top'
+    if (offsetTop != null && scrollTop <= offsetTop) return 'top'
     if (offsetBottom != null && (colliderTop + colliderHeight >= scrollHeight - offsetBottom)) return 'bottom'
 
     return false