WooCommerce Memberships 1.26.9

* Fix - Ensure products from all plans are shown when listing products that grant access to content in the restriction notices
* Fix - Do not restrict from access product categories that are only targeted by product purchase restriction rules
* Fix - Have `woocommerce_email_header` and `woocommerce_email_footer` action hooks pass the email object as hook parameter
* Fix - Always show public LearnDash content
* Fix - Address a JavaScript issue in the Setup Wizard screens

* Tweak - Allow merging existing user memberships in CSV imports without specifying a user membership ID if the user ID, login name or email address is provided in combination with the plan ID or slug
* Tweak - Ensure LearnDash course overview and status are hidden when restricted
* Tweak - Improve performance when generating restriction or discount notices that include products
* Tweak - Allow removing an installment plan flag on subscription-tied user memberships on CSV imports through an `installment_plan` column
* Fix - Ensure that if a variable product is excluded from receiving member discounts, all its variations are consistently excluded from discounts as well
* Fix - Ensure that the `customer` query var in User Memberships REST API requests to get user memberships by customer works consistently
* Fix - Pass the correct return type for the `display_post_states` filter callback
* Dev - Add WooCommerce debug logging when starting new user memberships CSV import jobs

* Fix - Ensure that the `wcm_restrict` shortcode can correctly parse optional attributes