fake-site fixtures has invalid packages in composer files

Problem/Motivation

While working on #3318625: Remove active composer fixture files in UpdaterFormTest @kunal.sachdev

1) Drupal\Tests\automatic_updates_extensions\Functional\UpdaterFormTest::testSuccessfulUpdate with data set "maintenance mode on, semver module" (true, 'semver_test', 'Semver Test', '8.1.0', '8.1.1')
Exception: Warning: Undefined array key "type"
Drupal\package_manager\ComposerUtility->getProjectForPackage()() (Line: 240)

This was because it was trying to read the `drupal/core` package from the files in package_manager/tests/fixtures/fake_site/vendor/composer

These do not have a type property.

Steps to reproduce

Proposed resolution

Ensure the packages in package_manager/tests/fixtures/fake_site/vendor/composer are valid.

Maybe by adding a test here \Drupal\Tests\package_manager\Kernel\FakeSiteFixtureTest

To basically call \Drupal\package_manager\ComposerUtility::getProjectForPackage and \Drupal\package_manager\ComposerUtility::getPackageForProject

we can use name we know will return null because there are no packages that can be returned. but we should assert it returns null.

I think now it would have an exception because of the problem above.

Remaining tasks

User interface changes

API changes

Data model changes