Bump x509-limbo and/or wycheproof in CI (#14580)

Co-authored-by: pyca-boringbot[bot] <pyca-boringbot[bot]+106132319@users.noreply.github.com>

Author: pyca-boringbot[bot]

.github/actions/fetch-vectors/action.yml

@@ -17,6 +17,6 @@ runs:
       with:
         repository: "C2SP/x509-limbo"
         path: "x509-limbo"
-        # Latest commit on the x509-limbo main branch, as of Mar 25, 2026.
-        ref: "23a7ab348f27efef72d429f4faa92a3d8c23f720" # x509-limbo-ref
+        # Latest commit on the x509-limbo main branch, as of Apr 02, 2026.
+        ref: "771c438d52821081966b34fff7eb4c517731b4ae" # x509-limbo-ref
         persist-credentials: false