Fail the gitlab job if we fail to upload the artifacts (#7861)

## Summary of changes

Fails the gitlab `publish` job if we fail to upload

## Reason for change

We have been silently failing, and it's blocking the release

## Implementation details

`exit 1` if we fail to upload

## Test coverage

This is the test. ~We're still broken, so this should fail.~


https://datadoghq.atlassian.net/browse/APMLP-722

Author: andrewlock

.gitlab-ci.yml

@@ -92,6 +92,10 @@ publish:
               Start-Sleep -Milliseconds 100
           }
       } while ($i -lt 3)
+      # If we got here, all retries failed – fail the job:
+      Write-Error "Failed to upload artifacts to S3 after $i attempts."
+      exit 1
+
 
 download-single-step-artifacts:
   stage: package