Fix Composer plugins error

[mglaman]

Thanks! This should be fixed in Drupal core, but let's get it fixed here. Related to #13

I'm having to do the following in my CI flows:

      -   name: Fix allow-plugins (8.9)
          if: ${{ matrix.drupal == '^8.9' }}
          run: |
              cd ~/drupal
              composer config --no-plugins allow-plugins.drupal/core-composer-scaffold true
              composer config --no-plugins allow-plugins.drupal/core-project-message true
      -   name: Fix allow-plugins
          run: |
              cd ~/drupal
              composer config --no-plugins allow-plugins.composer/installers true
              composer config --no-plugins allow-plugins.dealerdirect/phpcodesniffer-composer-installer true

[mglaman]

Fixed in another PR.