[11.x] [policy] Set Composer requirement for Drupal 11

The relevant security advisory is https://github.com/advisories/GHSA-7c6p-848j-wh5h

Given that we will introduce runtime requirements for Composer with Automatic Updates I think we should just set this to 2.7 now, given AU currently requires 2.6+ but all 2.6 releases are considered insecure.

I missed that the composer file was already upgraded to 2.7.0 in #3421371, I'll close the MR.

DamienMcKenna → closed merge request !7161

Given we already did this and released it in 10.2.4 I think this can be closed out as fixed.

Automatically closed - issue fixed for 2 weeks with no activity.