Describe the bug
Adding a "Pullquote" block is by default in "align center" but this option isn't available in the lignment list so when changed, we can't go back to align center.

To reproduce
Steps to reproduce the behavior:

1. Add a Pullquote block
2. Change alignment

Editor version (please complete the following information):

• WordPress version: 5.4.1, default Gutenberg, no extra plugins
• Fresh install, nothing else added or imported

With a Pullquote Block, align center is missing:

With an image, we have all options: