Incomplete checks for color contrast on text with webkit-line-clamp

### Product

axe-core

### Product Version

4.4.2

### Latest Version

- [x] I have tested the issue with the latest version of the product

### Issue Description

#### Expectation
No colour contrast violations should be reported when using `webkit-line-clamp` and inner span(s).

#### Actual
A colour contrast incomplete check is reported when using a combination of `webkit-line-clamp` and inner `span`.

#### How to Reproduce

The issue is exactly the same as https://github.com/dequelabs/axe-core/issues/2669 except that this time it happens with the `webkit-line-clamp` CSS property instead of `text-overflow: ellipsis`.

You can reproduce the issue at: https://output.jsbin.com/savapuvoti.