Add more logging for unexpected status codes.

[ehuss]

This adds some more logging in the saga to determine why diffing is not working as expected. For the cargo milestoning, all I see in the logs is:

Retrying after 0 seconds, remaining attepts 2
Retrying after 0 seconds, remaining attepts 1
Retrying after 0 seconds, remaining attepts 0

and then nothing. My theory is that it is returning some unexpected status code. The retry logic checks for !is_success() which only checks for codes 2xx, and then error reporting code only checks for error_for_status_ref, which is only 4xx and 5xx. My guess is that some other status code is slipping through? I'm really shooting in the dark since I can't reproduce the issue locally.

[ehuss]

I'm going to close since I'm pretty confident that #1819 will resolve this.