Follow-up from "Improve work items widget loading state and error handling"

@ameliabauerly suggested that we use a skeleton loader in the MR and Work Items widgets:

I did want to check in on the skeleton loading question for these cards, as I remember that being mentioned during one of the reviews, and I spotted that skeleton loaders are recommended for cards in Pajamas.

I know we're using the - rather than the skeleton loading currently. It seems like the cards themselves, and the text, load quite quickly so, immediately displaying the information that's available seems like it provides more immediate value than just defaulting to skeleton loading until all of the information is available to display. But, is in situations where the entire card is loading slowly, and not just the count - is it worth having a skeleton loader for that? I don't know how likely that is to happen, or if it's an either/or decision we need to make. But, I at least wanted to check in on that question so we had a solid rationale for whichever option we take. Thoughts?

Since I know this MR is making the behavior between the MR and Issue widgets consistent, this question is non-blocking for this particular MR. That being the case, I'll go ahead and add my approval. But, let me know your thoughts on skeleton loading and we can perhaps consider additional improvements separately!