Fix GOROOT not being set in devbox shell environment

When you don't have a global installation of go toolchain
and rely only on the one provided by devbox, there is no
GOROOT variable set, so even though the go binary is in
PATH, none of its commands work and fail with GOROOT not
found.

Author: domust

devbox.json

@@ -13,6 +13,9 @@
     "kind@0.27.0",
     "kubectl@1.32.2"
   ],
+  "env": {
+    "GOROOT": "$PWD/.devbox/nix/profile/default/share/go"
+  },
   "shell": {
     "init_hook": [
       "echo 'Welcome to devbox!' > /dev/null"