Bump x509-limbo and/or wycheproof in CI (pyca#11539)

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

Author: pyca-boringbot[bot]

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

@@ -16,5 +16,5 @@ runs:
       with:
         repository: "C2SP/x509-limbo"
         path: "x509-limbo"
-        # Latest commit on the x509-limbo main branch, as of Sep 03, 2024.
-        ref: "c77f95adb01d2d0f1389c52530201b75b1e8c82c" # x509-limbo-ref
+        # Latest commit on the x509-limbo main branch, as of Sep 04, 2024.
+        ref: "21e4b22c4b1b69cc956bd6bb0db2c3e40c3f46e9" # x509-limbo-ref