Build/Test Tools: Fix invalid styles data type PHP Warning in REST_Block_Type_Controller_Test::test_get_item_invalid().

Sets the `styles` block setting to an empty array in the `REST_Block_Type_Controller_Test::test_get_item_invalid()` test to resolve:

{{{
Warning: foreach() argument must be of type array|object, string given in wp-includes/class-wp-theme-json.php on line 835
}}}

Previously the test set the `styles` setting to a string value, which is incompatible. The problem surfaced after [55172] added a `foreach` to iterate the `styles`. The root cause was due to this test passing a string instead of an array.

Why?

`WP_Block_Type` `styles` property is documented as only accepting an array data type. At the time of this changeset, it does not validate before setting the property.

Code interacting with the property expects it to be an array data type. The PHP Warning alerts that of a doing it wrong when the incorrect data type is registered for the block type.

Follow-up to [55172], [48173].

Props tanjimtc71, hellofromTonya, kapilpaul.
Fixes #57706.
Built from https://develop.svn.wordpress.org/trunk@55342


git-svn-id: http://core.svn.wordpress.org/trunk@54875 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.2-beta2-55341';
+$wp_version = '6.2-beta2-55342';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.