fix: skip repos returning 404 instead of failing the matrix job

[mfahlandt]

Problem

When a repository's releases or tags API returns HTTP 404 (e.g. spiffe/vsecm-sdk-go), the current code calls exit 1, which hard-fails the entire matrix job. This cascades into job failures and cancelled runs for all other repos in that batch.

Fix

Detect the "status":"404" in the error response and treat it as a graceful skip:

• Log a ::warning:: so it's visible in the job output
• exit 0 so the matrix job continues processing other repos

Applies to both generate-sbom.yml (main CNCF jobs) and reusable-generate-sbom.yml (subproject batch jobs), for both the releases and tags API calls.

Signed-off-by: Mario Fahlandt mfahlandt@pixel-haufen.de