Always use current access token for (re)started uploads

[dschmidt]

This is a follow up ticket for #7072.

That PR fixes access token refresh in every currently known/possible scenario, with that it becomes more important to gracefully handle changed access tokens in upload queue handling.
We need to make sure that uploads started (or restarted, e.g., in case of errors) use the new access token and are never started with an outdated token.

[kulmann]

To be clear: this was already broken before that PR. While working on that PR it became clear that we need to fix this, but it was clearly out of scope for the PR.