cosmo-b support in a rack needs new sprockets

[leftwo]

After this lands, we need to bump omicrons pointer to sprockets.
oxidecomputer/sprockets#97

Without this, we don't support Cosmo-B sleds in a rack. The error in sled agent looks like:

00:57:51.859Z ERRO SledAgent (trust-quorum): Failed to accept a connection                                                   
    baseboard_id = 913-0000019:BRM42220030                                                                                   
    error = Failed to get PlatformId from cert chain: No PlatformId found in PkiPath                                         
    file = trust-quorum/src/connection_manager.rs:545