Add TinaCMS postMessage advisory references

[cookesan]

Adds TinaCMS postMessage advisory references to GHSA-g5qx-h5f3-mp2f.

Audit refresh, July 8, 2026:

• Confirmed the live PR is open, ready for review, merge-clean, and the visible advisory check is green.
• Rechecked the merge-base diff: exactly one advisory JSON file changes (advisories/github-reviewed/2026/06/GHSA-g5qx-h5f3-mp2f/GHSA-g5qx-h5f3-mp2f.json), JSON parses, git diff --check passes, and the exact-head worktree is clean.
• Revalidated the added public references in the diff; all resolve through their source site or registry.

[cookesan]

Refreshed on July 8, 2026:

• GHSA-g5qx-h5f3-mp2f and CVE-2026-55660 remain public and consistent with this advisory.
• Verified tinacms/tinacms PR [GHSA-gp2f-7wcm-5fhx] Craft CMS has Cloud Metadata SSRF Protection Bypass via DNS Rebinding #7056, commit c491fc55e612725f5d775eeb1fdf3f8ba82314fa, releases tinacms@3.9.3 and @tinacms/app@2.5.6, and the matching npm packages.
• Added the NVD advisory reference and nvd_published_at value after confirming the public NVD record.
• Local validation passed: jq empty and git diff --check.

No affected range, package, or severity changes are included.