Added missing custom class in the latest posts & categories block

[jorgefilipecosta]

Description

This PR adds a custom class in the front end in the latest post and categories block.
Fixes: #5644

How has this been tested?

Add a latest posts block, set a custom class, save the post verify the custom class appears in the front end (in master it does not appear).
Repeat the same steps for the categories block.

[gziolo]

Can you provide the same fix for Categories block? :D

From @jvisick:

This is similar to #5486. It also seems to be an issue with the categories widget block.

[jorgefilipecosta]

Thank you for reminding me I missed to commit the changes to the category block. They were added.

[gziolo]

Out of curiosity, how does it work without attributes specified on the server? :D

[jorgefilipecosta]

Hi @gziolo, I was also curious about this logic while doing the changes. This works because prepare_attributes_for_render, just returns the attributes parsed from the comment demarcations if the attributes are not "registered" on the server.

gutenberg/lib/class-wp-block-type.php

Lines 128 to 130 in eee9278

	if ( ! isset( $this->attributes ) ) {
	return $attributes;
	}

[gziolo]

Good to know, it needs to be fixed soon (another PR) :)

[gziolo]

phpcs complains about:

Array double arrow not aligned correctly; expected 7
| | space(s) between "'className'" and double arrow, but
| | found 6.
| | (WordPress.Arrays.MultipleStatementAlignment.DoubleArrowNotAligned)

[jorgefilipecosta]

phpcs complains about:

Hi @gziolo, I'm sorry, my editor because of some reason did not display the error, the problem was corrected.

[gziolo]

LGTM 👍

[jorgefilipecosta]

Thank you for the review @gziolo!

[aduth]

The introduction of this attribute should have been complemented by an update to fixtures, which auto-generates from server attributes. Running npm run fixtures:regenerate on master introduces an unexpected change.