fix(toast): Prevent actions text from wrapping to multiple lines

While working on https://gitlab.com/gitlab-org/gitlab-ee/issues/9102, which requires a toast message to be displayed with an Undo dismiss action, it appeared that an action's text might wrap to multiple lines when:

• the action's text contains multiple words
• the toast message is long enough for the toast to reach its max width

Current toast

To prevent this, white-space: nowrap; has been applied to toast actions, and a story has been added to demonstrate and test this fix.

Fixed toast