Check UpdateAddMediaTest::testMediaUpdate()

Added a relevant comment to the commit of the original PR here, but it's easy to miss, so adding as a comment here.

Can't see the specific code that breaks in the pipelines, but I believe this might be breaking due to the way the gutenberg_config_schema_info_alter() dynamically picks up schema fields at the moment (which isn't ideal).

At the point that $config_editable->set($key, $allowed_blocks)->save(); is called, Drupal attempts to validate the config according to the schema, but fails because the schema is still based off the "previous" config value before the media entity was enabled.

I believe since this is an update hook, switching to:

$config_editable->set($key, $allowed_blocks)->save(TRUE);

might yield better results since that won't trigger any config schema validation since we trust the data we pass into the updated config at that point.

But this begs a bigger question as to whether this crash due to new fields only happens under test environments, or will occur if you attempt to add Gutenberg support for new entity types on live sites (I don't believe it'll/should, but might need to explore further).

Here's a suggestion for re enabling it ✌️

I added the other update hook inside the test so now the config does not end up in the wrong format