bump fulcio and sigstore to fix CVE-2025-66506#4571

LaurentGoderre wants to merge 1 commit intosigstore:release-2.6sigstore/cosign:release-2.6from

LaurentGoderre:fix-CVE-2025-66506LaurentGoderre/cosign:fix-CVE-2025-66506Copy head branch name to clipboard