The upstream_sources.yml file needs to point to the correct branches in github repositories.

Currently they're set to release branches (e.g., releases/2.4.2). They need to switch to the HEAD of the branch (e.g. maistra-2.4).

Example: https://gitlab.cee.redhat.com/istio/cpaas/containers-midstream/-/blob/7278aa82df970045ca3f4b905286e6233f3309ca/upstream_sources.yml#L3

This needs to be done for containers and proxy midstream repos.