Miłosz Bieniek

LibWeb: Fix vertical alignment for flex container with `max-height`.

5

The [align-content-vert-001a](https://wpt.fyi/results/css/css-flexbox/align-content-vert-001a.html?product=ladybird) and [align-content-vert-002](https://wpt.fyi/results/css/css-flexbox/align-content-vert-002.html?product=ladybird) wpt tests pass because their `.flexbox` class has a `height` property. [align-content-vart-001b](https://wpt.fyi/results/css/css-flexbox/align-content-vert-001b.html?product=ladybird) fails because its `.flexbox` class has a `max-height` property instead. My changes fixes this...