testProcessOutbound fails on Drupal 11.1+

Problem/Motivation

Drupal\Tests\subpathauto\Kernel\SubPathautoKernelTest::testProcessOutbound fails on Drupal core 11.1 and later. The assertion /node/1/edit → /kittens/edit returns the path unchanged.

Root cause: the test's setUp() calls $this->container->get('path_alias.whitelist')->set('node', TRUE); to allow alias lookups for /node/*. Since Drupal 11.1, path_alias.whitelist is deprecated and is now a separate service instance from path_alias.prefix_list (the new service that AliasManager actually reads from).

The last green CI pipeline for `8.x-1.x` was 2024-11-29 on what was then Drupal 11.0/11.1. Between then and now, `path_alias.whitelist` was deprecated in 11.1 (→ `router.prefix_list`, see https://www.drupal.org/node/3467559) and several path-alias-related services were restructured. Outbound lookup for subpaths appears to have regressed as a side effect.

It's blocking every contrib MR's CI. See for example: #2964786: Ignore specific paths and #3603417: Automated Drupal 12 compatibility fixes for subpathauto 1.x-dev

Steps to reproduce

1. Run vendor/bin/phpunit web/modules/contrib/subpathauto/tests/src/Kernel/ on a site with Drupal core ≥ 11.1.

Proposed resolution

Fix tests/src/Kernel/SubPathautoKernelTest.php:

Remaining tasks

• Apply the two test changes.
• Confirm CI pipeline turns green on the issue branch.

User interface changes

None.

API changes

None.

Data model changes

None.