Fatal log messages have debug log level

[ghost]

What Renovate type, platform and version are you using?

Selfhosted

Describe the bug

When a push fails, the failure is logged with the debug log level. Not pushing means the bot isn't working, and I think that warrants a fatal, or error log, not debug.

Additionally, after such failure, exit code is still 0. This makes it hard to detect that the bot is no longer working (e.g. if it no longer has permissions). Failure should result in a non-zero exit code.

Relevant debug logs

DEBUG: Error commiting files (repository=*/*, branch=renovate/system.io.abstractions-12.x)
       "err": {
         "task": {
           "commands": [
             "push",
             "origin",
             "renovate/system.io.abstractions-12.x:renovate/system.io.abstractions-12.x",
             "--force",
             "-u",
             "--no-verify",
             "--verbose",
             "--porcelain"
           ],
           "format": "utf-8"
         },
         "message": "Pushing to https://*.visualstudio.com/*/*/_git/*\nPOST git-receive-pack (883 bytes)\nerror: failed to push some refs to 'https://*.visualstudio.com/*/*/_git/*'\n",

To Reproduce

Additional context

[rarkins]

I think a warn here is appropriate, not fatal or error