Description

Introduced in #3851 / badc344, this causes PHP warnings when using the Image block with Lightbox enabled.

Why?

The block_core_image_render_lightbox() function passes the results of wp_get_global_styles() directly to esc_attr().

wp_get_global_styles() can return an array, but esc_attr() works on strings.

Step-by-step reproduction instructions

1. Insert image block with lightbox (I was using the 2021 theme)
2. See warning

Screenshots, screen recording, code snippet

No response

Environment info

WP trunk

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