Custom Amounts UI placeholder shows additional spaces if these were added to store settings

[iamgabrielma]

If we add spaces to the currency separators under WooCommerce > Settings > General, these additional spaces can be seen in the placeholder amount when creating a custom amount to add to an order:

We still sanitize the fields correctly thanks to https://github.com/woocommerce/woocommerce-ios/pull/14057 , but the placeholder is not affected.