Check selector list for parent selectors in at-root-no-redundant

[pamelalozano16]

Fix false positive of redundant @at-root in selector list.
This example is identified as redundant, even though @at-root is useful for the second selector .a#{&}b .

@at-root .c &,
  .a#{&}b {
     color: black;
}

Here's a SCSS demo with examples.

[kristerkari]

Thanks!