Docs: Correct @return value for _get_block_templates_files().

[dilipbheda]

The _get_block_templates_files() function returns null, so we also need to add in inline code.

[mukesh27]

Hi there!

I thought we should add some description for return type.

@return array|null The Template files, or null if $template_type not matched.

[dilipbheda]

@mukesh27 Thank you for the review, I've updated the patch and uploaded it here.

[SergeyBiryukov]

In 58768:

Docs: Correct @return value for _get_block_templates_files().

The function returns null if $template_type is not wp_template or wp_template_part.

Follow-up to [52062].

Props dilipbheda, mukesh27.
Fixes #61705.