Use detected Project.PackageManager in reports

What does this MR do?

Change the Scanner so that it uses Project.PackageManager instead of Parser.PackageManager. Eventually this PackageManager attribute is used in the generated JSON report. This improves the accuracy of the package manager field in a case where:

• The Finder properly detects the package manager used in a Project.
• But the same Parser is used for multiple package managers.

What are the relevant issue numbers?

gitlab-org/gitlab#338252 (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