[BUGFIX] Ignore "composer/installers" requirement

Most extensions that already provide a composer.json file have a
requirement against composer/installers. Our Package Manager tries
to resolve that dependency and files. As the composer/installers
package is not required for an extension to work it is ignored until
the Extensionmanager can handle composer packages natively.

Resolves: #52767
Releases: 6.2
Change-Id: Ia6c57f6006958aadea759cd583f2dce7716be389
Reviewed-on: https://review.typo3.org/24785
Tested-by: Claus Due
Reviewed-by: Sebastian Fischer
Reviewed-by: Fabien Udriot
Tested-by: Fabien Udriot
Reviewed-by: Thomas Maroschik
Tested-by: Thomas Maroschik