ci: advance .ci microReticulum checkout to attested pin 921b3aa

The pyxis-pytest job checks out the microReticulum reference for the
NomadNet x86 client, whose CMake manifest attests the exact commit
(921b3aa, endpoint hot-path read gate). The workflow still pointed at
cd0338e, so the client configure aborted on the attestation check and
the pytest job failed before running tests. The native17 job (submodule)
is unaffected and already green.

.github/workflows/test.yml

@@ -20,7 +20,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: torlando-tech/microReticulum
-          ref: cd0338e7fc07d3a7785a450656ba766491cbf6e8
+          ref: 921b3aa030525f819671d99eff1d1f28350c9b69
           path: .ci/microReticulum
 
       - name: Set up Python