feat(tvix/store/protos): use Validate() function on root node

This updates the code to make use of the new Validate() function defined
on a Node.

Change-Id: I9b6ed694661f41e700f19cc78d53d2224b61852d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9718
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/default.nix

@@ -108,7 +108,7 @@ in
   store-protos-go = pkgs.buildGoModule {
     name = "store-golang";
     src = depot.third_party.gitignoreSource ./store/protos;
-    vendorHash = "sha256-qPtEQTd1Vol8vhE10AdwTleTLfYS7xaOir3Ti4MJ+Vc=";
+    vendorHash = "sha256-WAYaIT3h3Cdvo1RB8T7DuoxeKvXfkq8vo/vdkhJQDs0=";
   };
 
   # Build the Rust documentation for publishing on docs.tvix.dev.