chore(deps): bump quinn-proto 0.11.14 → 0.11.15 (RUSTSEC-2026-0185) (#5562)

Lockfile-only bump to clear the security-audit CI job. quinn-proto
v0.11.14 is vulnerable to remote memory exhaustion from unbounded
out-of-order stream reassembly (RUSTSEC-2026-0185, fix >=0.11.15);
it is a transitive dep via the reqwest/quinn HTTP/3 stack. No other
dependency churn.

Co-authored-by: Ralph Küpper <ralph2@skelpo.com>

Author: proggeramlug