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

nix/buildGo/default.nix

@@ -118,4 +118,7 @@ in
   program = makeOverridable program;
   package = makeOverridable package;
   external = makeOverridable external;
+
+  # re-expose the Go version used
+  inherit go;
 }