Add python-multipart querystring DoS fix references

[cookesan]

Adds python-multipart querystring DoS fix references to GHSA-5rvq-cxj2-64vf.

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-5rvq-cxj2-64vf/GHSA-5rvq-cxj2-64vf.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]

Maintainer audit: this only expands the reference set for the python-multipart querystring DoS advisory. Kludex/python-multipart#290 is merged, commit d69df35cd2cad9c72794c2c340db646afae957d8 resolves, release tag 0.0.30 resolves, and python-multipart 0.0.30 is available on PyPI and not yanked. The advisory JSON parses, the committed diff passes git diff --check, the PR is merge-clean, and advisory processing is successful. No package, affected range, severity, or database metadata is changed.