Adding validate phase to the CI

Adds a validate phase to the CI which runs a linter. Also fixes
linter issues discovered during the initial run

scripts/validate.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+set -e
+golangci-lint run
+go mod tidy
+go mod verify
+unclean=$(git status --porcelain --untracked-files=no)
+if [ -n "$unclean" ]; then
+  echo "Encountered dirty repo!";
+  echo "$unclean";
+  exit 1;
+fi