Add ASP.NET Core CVE-2024-21319 references

[cookesan]

Adds Microsoft.IdentityModel and System.IdentityModel fixed NuGet package references, plus the NVD reference for CVE-2024-21319, to GHSA-59j7-ghrg-fj52.

Audit refresh, July 8, 2026:

• Confirmed GHSA-59j7-ghrg-fj52 maps to CVE-2024-21319, and NVD has a record for CVE-2024-21319.
• Confirmed fixed NuGet package pages for versions 5.7.0, 6.34.0, and 7.1.2 for both affected packages resolve.
• Local checks passed: one advisory JSON file changed in the PR diff, JSON parses, git diff --check passes, and the worktree is clean.