ci: verify go fix leaves tree clean

Author: AzraelSec

.github/workflows/ci.yml

@@ -13,6 +13,11 @@ jobs:
         with:
           go-version: '1.26'
 
+      - name: Verify go fix is clean
+        run: |
+          go fix ./...
+          git diff --exit-code
+
       - name: Build
         run: go build -v ./...