Customizer hangs on the "downloading" full overlay when closing the FTP credentials modal

[afercia]

Splitting this out from https://core.trac.wordpress.org/ticket/42205#comment:11

• force the FTP modal to appear as described in #42205
• apply the patches from #42205 and #42184 if not merged yet
• go to the Customizer > change theme > wp.org themes
• click on theme details to open the details modal and then install
• or click directly on Install & Preview
• the FTP modal opens correctly

However, when closing the modal (press "Cancel") the Customizer hangs on the "downloading" full overlay, see screenshot below. There's no escape from there, the only chance is refresh or browser's Back button:

[westonruter]

In addition to dismissing the notification on request.fail() we also need to dismiss when the credentials are requested. This is the code that would need to be updated: ​https://github.com/WordPress/wordpress-develop/blob/a719234/src/wp-admin/js/customize-controls.js#L3167-L3179

[celloexpressions]

This is the primary thing that #42184 addresses (per the ticket description) and is fixed in yesterday's patch there.