Bump x509-limbo and/or wycheproof in CI (#13243)

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 Aug 01, 2025.
-        ref: "7b9bda64eb41ce785be247c77fe080c663a029e3" # x509-limbo-ref
+        # Latest commit on the x509-limbo main branch, as of Aug 05, 2025.
+        ref: "b640f7ad6ad9f97c7708ee1f9cf773fef80ec572" # x509-limbo-ref