preview-format prop does not work

[bbraun92]

Describe the bug
Try passing a string to the preview-format prop. The preview text in the calendar does not follow the format.

To Reproduce
See playground for reproduction.
https://stackblitz.com/edit/vuepic-vue-datepicker-b9dzoy?file=src%2Fcomponents%2FPlayground.vue,package.json

Expected behavior
Format in preview bit of the calendar follows the format rule.

Screenshots

Desktop & mobile (please complete the following information):

• Browser Chrome 127.0.6533.73 on MacOS 14.4.1
• Library version 9.0.1