fix(ci): handle missing go.sum gracefully

.github/workflows/ci_arch.yml

@@ -11,6 +11,8 @@ jobs:
     runs-on: ubuntu-latest
     container:
       image: archlinux:latest
+    env:
+      CGO_ENABLED: "0"
     steps:
       - uses: actions/checkout@v4
       - name: Install dependencies
@@ -23,7 +25,11 @@ jobs:
       - name: Verify go.mod tidy
         run: |
           go mod tidy
-          git diff --exit-code go.mod go.sum
+          if [ -f go.sum ]; then
+            git diff --exit-code go.mod go.sum
+          else
+            git diff --exit-code go.mod
+          fi
       - name: Build
         run: go build ./...
       - name: Test