fix(cli): show info message only when --scanners is available

[knqyf263]

Description

trivy convert shows the following message even though it doesn't have --scanners flag.

Before

$ trivy convert -f cyclonedx /tmp/with_vulns.json -o /dev/null
2024-06-27T07:33:52+04:00       INFO    "--format cyclonedx" disables security scanning. Specify "--scanners vuln" explicitly if you want to include vulnerabilities in the CycloneDX report.

After

$ trivy convert -f cyclonedx /tmp/with_vulns.json -o /dev/null

Related issues

• Discussion: Unknown flag Error when converting JSON to cyclonedx #7016

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[DmitriyLewen]

LGTM.