`shiny.express.ui.card` doesn't render card items properly

[cpsievert]

For example:

from shiny.express import ui

with ui.card():
    ui.card_header("Header")
    "Body"

Both the header and the body are being wrapped in a .card-body, which is leading to the extra, unwanted, padding.

[wch]

For reference, this is what it's supposed to look like (with the DOM structure below):

---

And this is what it looks like on main: