Content Block: update block name in placeholder content

[liviopv]

Description

The placeholder text that shows up for the block when editing a template still uses "Post Content Block" as the name

Step-by-step reproduction instructions

1. Add a Content Block
2. Look into the placeholder text

Screenshots, screen recording, code snippet

Environment info

• WordPress 6.3, GB 16.5 RC1

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[jordesign]

Just tested with WP 6.3 and GB 16.5 and can confirm this is in place

[jordesign]

Closing this as a fix is merged in #53902