Increase log level when `dotnet add` fails

What does this MR do?

SAST analyzer error with .NET - Unable to build... (gitlab-org/gitlab#349615 - closed) reports a number of issues (both resolved and unresolved) that manifest with a single log line:

Unable to build project using `dotnet`

Upon examination, the code paths that lead here all would produce logs at or above the default level, except the dotnet add branch.

Hence, to help disambiguate which issues are actually in play and make debugging easier, I felt it would be useful to increase the log level for the branch that is currently only at Debug.

What are the relevant issue numbers?

Contributes to (but does not directly solve) gitlab-org/gitlab#349615 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer