doc: fix source link margin to sub-header mark

Prior to this commit, [src] link overlapped sharped (#) sub-header link
PR-URL: #33664
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: rodion-arr

doc/api_assets/style.css

@@ -342,6 +342,7 @@ h5 {
 .srclink {
 float: right;
 font-size: smaller;
+margin-right:30px;
 }
 
 h1span,