chore: check go.mod and run gofmt in CI

.github/workflows/lint.yaml

@@ -5,6 +5,19 @@ on:
     types: [opened, edited, synchronize, reopened]
 
 jobs:
+  go-mod:
+    name: Check go.mod
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version: stable
+      - name: Check go mod
+        run: |
+          go mod tidy
+          git diff --exit-code go.mod
+          git diff --exit-code go.sum
 
   lint:
     name: Lint
@@ -14,6 +27,15 @@ jobs:
     - name: Check out code into the Go module directory
       uses: actions/checkout@v4
 
+    - uses: actions/setup-go@v5
+      with:
+        go-version: stable
+
+    - name: Run gofmt
+      run: |
+        find . -type f -name '*.go' -not -path './testdata/*' -exec gofmt -w {} +
+        git diff --exit-code
+
     - name: Run Revive Action
       uses: morphy2k/revive-action@v2
       with: