Report authentication errors when pulling from SSH remote

[isc-pbarton]

If I try to pull from an SSH remote with ##class(SourceControl.Git.API).Pull() and my SSH key is not accepted, there are no errors reported. The return status is ok and the output looks like:

Pulling from branch: main
Fetch done
Files that will be modified by git pull:
    None

We should check for errors in the git fetch and output them to the user.

[isc-pbarton]

I'm not able to replicate this anymore. I'm sure it's been addressed by other changes this year.