Set up govulncheck for autosign

.github/workflows/autosign-govulncheck.yml

@@ -0,0 +1,21 @@
+name: govulncheck
+
+on:
+  push:
+    branches:
+      - 'main'
+    paths:
+      - 'autosign/**'
+  workflow_dispatch:
+
+jobs:
+  govulncheck_job:
+    runs-on: ubuntu-latest
+    name: Run govulncheck
+    steps:
+      - id: govulncheck
+        uses: golang/govulncheck-action@v1
+        with:
+           go-version-input: 1.20.6
+           go-package: ./...
+           work-dir: autosign