[6.x] Fix $fakeStacheDirectory path when running addon tests on Windows

[duncanmcclean]

This PR fixes an issue caused by the changes in #13640, where running addon tests on Windows would fail due to invalid paths:

Example failure:

1) Tests\Cart\Calculator\ApplyDiscountsTest::automatically_applies_discounts_without_codes
ErrorException: file_put_contents(D:/a/statamic-cargo/statamic-cargo/src/../tests/__fixtures__/dev-null/D:/a/statamic-cargo/statamic-cargo/tests/__fixtures__/content/collections/products.yaml): Failed to open stream: No such file or directory

D:\a\statamic-cargo\statamic-cargo\vendor\laravel\framework\src\Illuminate\Foundation\Bootstrap\HandleExceptions.php:258
D:\a\statamic-cargo\statamic-cargo\vendor\laravel\framework\src\Illuminate\Filesystem\Filesystem.php:204
D:\a\statamic-cargo\statamic-cargo\vendor\statamic\cms\src\Filesystem\AbstractAdapter.php:29
D:\a\statamic-cargo\statamic-cargo\vendor\statamic\cms\src\Filesystem\Manager.php:49
D:\a\statamic-cargo\statamic-cargo\vendor\laravel\framework\src\Illuminate\Support\Facades\Facade.php:363
D:\a\statamic-cargo\statamic-cargo\vendor\statamic\cms\src\Data\ExistsAsFile.php:94
D:\a\statamic-cargo\statamic-cargo\vendor\statamic\cms\src\Stache\Stores\BasicStore.php:142
D:\a\statamic-cargo\statamic-cargo\vendor\statamic\cms\src\Stache\Stores\BasicStore.php:114
D:\a\statamic-cargo\statamic-cargo\vendor\statamic\cms\src\Stache\Repositories\CollectionRepository.php:87
D:\a\statamic-cargo\statamic-cargo\vendor\laravel\framework\src\Illuminate\Support\Facades\Facade.php:363
D:\a\statamic-cargo\statamic-cargo\vendor\statamic\cms\src\Entries\Collection.php:505
D:\a\statamic-cargo\statamic-cargo\tests\Cart\Calculator\ApplyDiscountsTest.php:126
D:\a\statamic-cargo\statamic-cargo\tests\Cart\Calculator\ApplyDiscountsTest.php:21

This PR fixes the issue by wrapping the path in Path::resolve() to ensure the dots in the path are correctly resolved. I've tested this fix on one of my addons:

• Failing tests: https://github.com/duncanmcclean/statamic-cargo/actions/runs/21442231562/job/61748158259
• Commit between tests: duncanmcclean/statamic-cargo@377cc4c
• Passing tests: https://github.com/duncanmcclean/statamic-cargo/actions/runs/21442316287/job/61748469285