CheckoutModal: Ensure cancel_to and redirect_to are relative urls

[lsl]

Fixes https://github.com/Automattic/dotcom-forge/issues/9902 Follows up on https://github.com/Automattic/wp-calypso/pull/96514

Proposed Changes

• Wraps redirects for cancel_to and redirect_to in isRelativeUrl checks within the checkout modal.

Testing Instructions

• http://calypso.localhost:3000/setup/assembler-first/new-or-existing-site
• Select new or existing site
• Continue through until there is an option to choose a premium style, choose one
• Continue until prompted to upgrade to a personal plan, click to upgrade
• Modify the redirect_to param in the url to something like example.com
• Make a purchase using store sandbox or credits
• Redirect should load previous route with args instead ... ? (currently not working as expected, it reloads the checkout modal not the previous screen)

Note, to skip assembler setup you can load the url directly (swapping site for a site with free plan): http://calypso.localhost:3000/setup/assembler-first/pattern-assembler?siteSlug=testingcalypso16.wordpress.com&siteId=239255304&screen=upsell&header_pattern_id=15892&footer_pattern_id=15364&color_variation_title=Pearl

[github-actions[bot]]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-125376

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-125376&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-125376&env=a8c-for-agencies

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~7 bytes added 📈 [gzipped])

``` name parsed_size gzip_size checkout +12 B (+0.0%) +7 B (+0.0%) ``` Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Async-loaded Components (~31 bytes added 📈 [gzipped])

``` name parsed_size gzip_size async-load-calypso-my-sites-checkout-modal +121 B (+0.0%) +24 B (+0.0%) async-load-calypso-layout-masterbar-checkout +12 B (+0.0%) +7 B (+0.0%) async-load-calypso-blocks-editor-checkout-modal +12 B (+0.0%) +7 B (+0.0%) ``` React components that are loaded lazily, when a certain part of UI is displayed for the first time.

Legend

What is parsed and gzip size?

**Parsed Size:** Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory. **Gzip Size:** Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug update/cancel_to2 on your sandbox.