Tests: Declare `custom-logo` theme support for custom logo tests.

This addresses failures in `has_custom_logo()` and `get_custom_logo()` tests when being run separately:
{{{
1) Tests_General_Template::test_has_custom_logo
Custom logo should not be set after removal.
Failed asserting that true is false.
tests/phpunit/tests/general/template.php:291

2) Tests_General_Template::test_get_custom_logo
Custom logo should not be set after removal.
Failed asserting that a string is empty.
tests/phpunit/tests/general/template.php:336
}}}

Specifically, this ensures that the `site_logo` option gets deleted in `_delete_site_logo_on_remove_theme_mods()`, which in turn prevents the `core/site-logo` block filters from affecting the custom logo tests.

Alternatively, these filters could be removed instead:
{{{
remove_filter( 'theme_mod_custom_logo', '_override_custom_logo_theme_mod' );
remove_filter( 'pre_set_theme_mod_custom_logo', '_sync_custom_logo_to_site_logo' );
}}}

Follow-up to [36905], [51091], [51421], [52042].

See #55652.
Built from https://develop.svn.wordpress.org/trunk@53774


git-svn-id: http://core.svn.wordpress.org/trunk@53333 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-alpha-53773';
+$wp_version = '6.1-alpha-53774';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.