postgresql: fetch from GitHub instead of tarball

This allows us to fetch newer releases a few days before they are
officially released and the tarballs have been pushed.

The regular release cycle is like this:
- Sunday, the release notes are committed.
- Monday, the version is "stamped", i.e. the version bump committed.
- Thursday, the release is made.

There are not going to be any changes from Monday on, so we can kick off
our builds at that time already - they still need time to hit unstable
anyway.

0 files changed, 0 insertions, 0 deletions