fix: explicitly handle exhausted Trivy retries

[Yashh56]

Changes

This PR fixes a bug in the image vulnerability scanning retry logic.

Previously, if all 10 retry attempts to download the Trivy vulnerability database failed, the loop would exit and incorrectly fall through to json.Unmarshal. Because the output contained the plain text connection error instead of valid JSON, this would cause a confusing JSON parsing panic (invalid character...) that masked the real execution error.

This PR:

1. Adds an explicit check after the loop to return the underlying Trivy execution error if all retries are exhausted.
2. Cleans up a redundant i < 10 check inside the for i := 0; i < 10; i++ loop.

Related Issue

Fixes #2329

Type of PR

/kind bug

Submitter Checklist

• Includes tests if functionality changed/was added
• Includes docs if changes are user-facing
• Kind label has been set
• Release notes block has been filled in, or marked NONE

Release Notes

Fixed an issue where vulnerability scanning failures caused by Trivy database download timeouts would result in a confusing JSON parsing error instead of correctly reporting the underlying connection issue.

[openshift-ci]

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[kaizakin]

/lgtm