ci: check for go mod tidy (#741)

This ensures that go.mod is always tidied.

.github/workflows/ci.yml

@@ -69,3 +69,23 @@ jobs:
 
       - if: failure()
         run: echo "::error::Check failed, please run 'go generate ./...' and commit the changes."
+
+  go-mod-tidy:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+
+      - name: Run go mod tidy
+        run: go mod tidy
+
+      - name: Check uncommitted changes
+        run: git diff --exit-code
+
+      - if: failure()
+        run: echo "::error::Check failed, please run 'go mod tidy' and commit the changes."

renovate.json

@@ -1,4 +1,5 @@
 {
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
-  "extends": ["github>hetznercloud/.github//renovate/default"]
+  "extends": ["github>hetznercloud/.github//renovate/default"],
+  "postUpdateOptions": ["gomodTidy"]
 }