Grant write permissions for GC to all repositories

[trask]

So that we can transfer issues to other repositories as needed when doing issue triage in the specification repository.

This is independent from #2025, since that PR will grant the (higher) org admin rights to just a couple of GC members, while all GC members take part in spec triage.

[reyang]

I've made the update to all the current repositories (except for temp ones created for security vulnerability hotfixes and the archived ones).