Accessibility issue with shortcut panel close button

**react-dates version**
e.g. react-dates@18.3.1

**Describe the bug**
When focus on input and we open shortcut panel through shift + ? shortcut there's no focus on the close button so we can't close it by hitting enter


**Steps to reproduce the behavior**
- Click on the either input to open calendar
- Press shift + ? shortcut to open shortcut panel
- Note that there's no focus on the close button so we can't close that by hitting enter

**Screenshots/Gifs**
<img width="643" alt="image" src="https://.com/react-dates/react-dates/assets/100914918/5d5486db-5529-42bb-98bd-3425264fba71">
<img width="661" alt="image" src="https://.com/react-dates/react-dates/assets/100914918/8504b436-2aee-4dd0-a272-26da5bb8483e">

**Is the issue reproducible in Storybook?**
Yes, for example https://react-dates..io/react-dates/?path=/story/daterangepicker-drp--default

Description