Caption of ToggleSwitchForm is given too little space

[HDinger]

Steps to reproduce

• Go to https://primer-lookbook.github.com/view-components/lookbook/inspect/primer/forms/example_toggle_switch_form
• Decrease the window size, so that the label is wrapped

Buggy behaviour

• The caption is limited to width of the label

Expected

Taken from the docs, the caption should span the whole witdh of the toggle switch form and not be limited to the width of the label

[jonrohan]

Nice catch! We'll take a look, I think we could update the container to not get squashed like that