ci: add job to ensure that the go.sum is up to date with the go.mod file

Signed-off-by: deadprogram <ron@hybridgroup.com>

.github/workflows/linux.yml

@@ -12,6 +12,24 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  go-mod-tidy:
+    # Check that go.sum is up to date.
+    runs-on: ubuntu-slim
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+        with:
+          submodules: true
+      - name: Install Go
+        uses: actions/setup-go@v6
+        with:
+          go-version: '1.26.4'
+          cache: true
+      - name: Run go mod tidy
+        run: go mod tidy
+      - name: Check go.mod and go.sum are up to date
+        run: git diff --exit-code
+
   build-linux:
     # Build Linux binaries, ready for release.
     # This runs inside an Alpine Linux container so we can more easily create a