Don't report errors when validated with @supports

https://developer.mozilla.org/en-US/docs/Web/CSS/@supports

```
@supports (content-visibility: hidden) {
	.foo {
		content-visibility: hidden;
	}
}
```

This shouldn't report an error. Same also for e.g. `@supports (content-visibility: hidden) and (display: flex) {`
Any `or` conditions or if prefixed with `not` should continue to report errors just like now.