Use a fixed reference date in the Mistral3 contract

prototype-fleet.lock

@@ -293,12 +293,12 @@
     "mic-mistral3": {
       "integration": {
         "repo": "huggingface-mic/mistral3-mic",
-        "revision": "6320652c65d41c49903fe19d7cc2e5c0ab2842ad",
-        "files_sha256": "2923ae62a9857e187b4417d046b88acc02a9027f0a892427f8375eaff93efe41"
+        "revision": "5d6b31a7548b1dc4c1255f42cbe8d1d44ead6261",
+        "files_sha256": "52558c71b08b729cc8b943a0f1515ab7d162415117ba29f361a4d7c985c3d5fc"
       },
       "fixtures": {
         "huggingface-mic/mistral3-mic": {
-          "revision": "6320652c65d41c49903fe19d7cc2e5c0ab2842ad",
+          "revision": "5d6b31a7548b1dc4c1255f42cbe8d1d44ead6261",
           "files_sha256": "e1ff61844c87c8150ada71205f60c96b9aaf1782f951ea8377a0555446e6d41a",
           "target": "mistral3-mic"
         }