Update Guzzle psr7 advisory references

[cookesan]

Updates Guzzle psr7 advisory references in GHSA-vm85-hxw5-5432.

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-vm85-hxw5-5432/GHSA-vm85-hxw5-5432.json), JSON parses, git diff --check passes, and the exact-head worktree is clean.
• Revalidated the added public references and package-version evidence in the diff; all resolve through their source site or registry.

[cookesan]

Rechecked this PR while keeping the open Advisory Database queue current.

• The patch adds Guzzle psr7 pull request, commit, release, and NVD references.
• Pull request guzzle/psr7#798 is merged, and the fix commit resolves to f3f94b4d344fa9788afb9558ac032923a9767380.
• The release tag resolves as 2.12.1, matching the advisory fixed version.
• NVD CVE-2026-55766 is active, so the PR also fills nvd_published_at.

No affected ranges, package names, or severity fields are changed.