aria-allowed-attr ignore aria-multiline=false on element with contenteditable

[WilcoFiers]

We've seen examples where devs have put aria-multinline=false on elements with contenteditable, with a role that doesn't support them. The reason for this turns out to be that Safari will otherwise announce that element as being a multinline element. We've seen this on an element with role=combobox, but it would be good to test whether this behavior happens with other roles too.

At least the following should pass axe-core:

<!-- This passes -->
<div aria-multiline="false" tabindex="0" aria-labelledby="foo" role="combobox" contenteditable>

[straker]

If there are more than one not allowed attr and some are falsey values and some are violations, we'll ignore the incomplete cases as to not report on false positives. Once the violations are resolved and there are no more to report on for the node, we'll report on the incomplete cases.