chore(tools/depotfmt): use Go version from buildGo

This is required because Go 1.18 is actually being deleted. I've
applied the formatting breakage that it introduces (such as breaking
comment formatting), because I can't be bothered to try and work
around broken Go stuff.

Change-Id: Ica7cee0d01228845d6a766079fef36df99a3da96
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9832
Autosubmit: tazjin <tazjin@tvl.su>
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tools/depotfmt.nix

@@ -9,10 +9,9 @@ let
     echo "$@" | xargs -n1 ${pkgs.terraform}/bin/terraform fmt
   '';
 
-  # TODO: Upgrade to Go 1.19 and reformat tree
   config = pkgs.writeText "depot-treefmt-config" ''
     [formatter.go]
-    command = "${pkgs.go_1_18}/bin/gofmt"
+    command = "${depot.nix.buildGo.go}/bin/gofmt"
     options = [ "-w" ]
     includes = ["*.go"]