css content alt text is ignored

### Product

axe-core

### Product Version

4.10.3

### Latest Version

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

### Issue Description

#### Expectation
I want to use the alt text for the content attribute as described here: https://developer.mozilla.org/en-US/docs/Web/CSS/content
I would expect that axe detects the alt text.

#### Actual
Axe ignores the alt text.

#### How to Reproduce
Open in a browser and scan with axe browser extension

```html

.with-content {
content: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='100' height='100'%3E%3Ccircle cx='50' cy='50' r='40' fill='blue' /%3E%3C/svg%3E") /
"Alt text not detected"
}

```

Will report an issue, but is valid. At least chrome and FF show the alt text in their a11y trees.

#### Additional context
I opened a similar issue for playwright: https://github.com/microsoft/playwright/issues/35737