[TASK] Update composer v2 error message in runTests.sh

composer v2 is no longer an experimental feature of
Docker Desktop for MacOS/Windows. Broken composer v2
error message should be updated to give proper actual
information how to disable it correctly.

Resolves: #97489
Releases: main, 11.5, 10.4
Change-Id: I7c4199e5d3d3c47bbadba8210cc96b0385ab6fcc
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74448


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Jonas Eberle <flightvision@googlemail.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Jonas Eberle <flightvision@googlemail.com>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>