Unable to add new lines in paragraph with template_lock = 'all'

[pwkip]

Describe the bug

If you create a template lock like this:

$args = [
  'template_lock' => 'all',
  'template' => [[ 'core/paragraph' ]],
];

It is impossible to add new lines in the paragraph.
In non-locked paragraphs, you can add <br> by pressing Shift+Return

To reproduce

1. Create a post type with a template_lock = 'all', and template= [[core/paragraph]]
2. Try to add a new line in the paragraph by pressing Return and Shift+Return

Expected behavior

I expect a new line to appear when I press Return or Shift+Return

Screenshots

Editor version

• WordPress 5.4.1
• gutenberg plugin 8.1.0

Desktop

• OS: Ubuntu 20.04
• Chrome