[css-break] Ruby containers are not monolithic

[Loirooriol]

CSS break says

inline-block and inline-table boxes (and other inline-level display types that establish a new formatting context) may also be considered monolithic.

Ruby containers are inline-level and establish a new ruby formatting context. But I think they are not monolithic, because a ruby can break across lines.

Instead, I would say something like

atomic inlines (like inline-block and inline-table boxes) may also be considered monolithic.

Related: #1180

[fantasai]

Fixed by replacing “new formatting context” with “independent formatting context”.