\Drupal\BuildTests\Composer\Template\ComposerProjectTemplatesTest::testTemplateCreateProject breaks with composer 2.8.1

Caused by https://github.com/composer/composer/pull/12109 (reported there)

Looks like it's 2.8.1 specific issue so we can stick to 2.8.0 https://github.com/composer/composer/issues/12150

I think another test is also affected:

---- Drupal\Tests\Composer\Plugin\Scaffold\Functional\ComposerHookTest ----
Status    Group      Filename          Line Function                            
--------------------------------------------------------------------------------
Exception Other      phpunit-1.xml        0 Drupal\Tests\Composer\Plugin\Scaffo
    PHPUnit Test failed to complete; Error: PHPUnit 10.5.35 by Sebastian
    Bergmann and contributors.
    
    Runtime:       PHP 8.3.12
    Configuration: /builds/security/drupal-security/core/phpunit.xml.dist
    
    E..                                                                 3 / 3
    (100%)
    
    Time: 00:03.088, Memory: 8.00 MB
    
    There was 1 error:
    
    1)
    Drupal\Tests\Composer\Plugin\Scaffold\Functional\ComposerHookTest::testComposerHooks
    RuntimeException: Exit code: 1
    
    Creating a "fixtures/drupal-drupal" project at "./create-project-test"
    Installing fixtures/drupal-drupal (1.0.0)
    
    In PathDownloader.php line 51:
                                                                               
       
      Source path "./drupal-drupal" is not found for package
    fixtures/drupal-drupal                                                                       

AFAICS doing composer self-update 2.8.0 looks like it should be a good workaround until this is resolved upstream.

...that is assuming composer does revert the change. If not, we may have to make more significant changes.

I fixed default version in image to 2.8.0 to prevent re-queue of jobs according to https://git.drupalcode.org/issue/drupal-3479446/-/pipelines

the upstream comment

has 2 guesses abaout caouse commits for phar executable can be patched and tested