fix(users/flokli/nixos-tvix-cache): BindPaths is serviceConfig

Putting this into UnitConfig won't work, so the bind mount didn't
happen, causing the blobs to be created on the SSD too.

This was already deployed and the data migrated over.

Change-Id: Ie30c8f458cdad8b764817a48a048ec3ca3c18e64
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12922
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

users/flokli/nixos/nixos-tvix-cache/nar-bridge.nix

@@ -118,12 +118,12 @@
     unitConfig = {
       # Keep most data on the SSD which is at /var/lib/nar-bridge, but bind-mount the blobs in
       RequiresMountsFor = "/tank";
-      BindPaths = [
-        "/tank/nar-bridge/blobs.object_store:/var/lib/nar-bridge/blobs.object_store"
-      ];
     };
 
     # twice the normal allowed limit, same as nix-daemon
     serviceConfig.LimitNOFILE = "1048576";
+    serviceConfig.BindPaths = [
+      "/tank/nar-bridge/blobs.object_store:/var/lib/nar-bridge/blobs.object_store"
+    ];
   };
 }