update composition of Steering Committee

[boegel]

During the meeting of the (then still initial) EasyBuild Steering Committee on 29 June 2026, a couple of changes came into affect:

• We transitioned from Initial Steering Committee to Steering Committee;
• Simon (@branfosj) and Sam (@smoors) resigned as Steering Committee members, after approving the governance documents in document EasyBuild governance #374);
• Jörg (@sassy-crick), Bart (@bartoldeman), and Cintia (@WilleBell) were voted in as new Steering Committee members.