chore(whitby): Double the number of build agents again

The main bottleneck of our builds right now is Nix evaluation, which
means that most of the time is spent idling during builds.

Since we're evaluating in parallel, lets give it a few more builders.

I don't want to go all the way to 64 immediately to first see if we
get any adverse effects from highly concurrent builds running
concurrently (if we do we could group them into different "concurrency
groups" in Buildkite).

Change-Id: Ibc3f89fb59cb4ee471b152ff36887ffe2b39f8f8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1932
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

ops/nixos/whitby/default.nix

@@ -186,7 +186,7 @@ in lib.fix(self: {
       tokenPath = "/etc/secrets/buildkite-agent-token";
       hooks.post-command = "${buildkiteHooks}/bin/post-command";
     };
-  }) (range 1 16));
+  }) (range 1 32));
 
   # Start a local SMTP relay to Gmail (used by gerrit)
   services.depot.smtprelay = {