Add h3 basic auth timing fix reference

[cookesan]

Adds h3 basic auth timing fix reference to GHSA-26f5-8h2x-34xh.

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/2026/03/GHSA-26f5-8h2x-34xh/GHSA-26f5-8h2x-34xh.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]

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

• The patch only adds the h3 basic auth timing fix commit reference; it does not change affected ranges, package metadata, or severity.
• The commit resolves to 4e091a6baadb7fe3708f3485b94b85c6457643d3.
• The commit subject matches the timing-fix context: fix(basic-auth): use jitter and constant-time string comparison (#1283).

No other advisory fields are changed.