queue-runner: don't decode base64 hostkey in hydra

Nix expects a base64 encoded hostkey in SSHMaster, so make sure we don't
decode this prematurely in hydra.

Reported-By: Puck Meerburg <[email protected]>

src/hydra-queue-runner/hydra-queue-runner.cc

@@ -171,7 +171,7 @@ void State::parseMachines(const std::string & contents)
             std::move(mandatoryFeatures),
             // `sshPublicHostKey`
             tokens[7] != "" && tokens[7] != "-"
-                ? base64Decode(tokens[7])
+                ? tokens[7]
                 : "",
         });