Various places during the `gh pr merge` flow show the PR number and
title. Those places are updated to also show the owner/repo.

E.g.
Before:
  Pull request #123 (title) is ready to be merged
After:
  Pull request owner/repo#123 (title) is ready to be merged

There are other places, where only the number is displayed. Those were
intentionally left as is. It made sense to show the owner/repo only when
the extra context of the title was present.

It also fixes the related tests.

cc #8777