Perform layout_builder_entity_presave for content entities only.

I encountered the same problem as described here: https://www.drupal.org/project/context/issues/3043383 →
When I saw in stacktrace layout_builder_entity_presave, I understand, what is the reason of this bug: Context is config entity, so Layout Builder could not be applied to it and there is no need to perform something on config entities presave.
So we need to change this condition

if (\Drupal::moduleHandler()->moduleExists('block_content')) {
...
}

to this

if ($entity instanceof ContentEntityInterface && \Drupal::moduleHandler()->moduleExists('block_content')) {
...
}