ghactions: Add snyk code scanning

This follows the instructions at https://github.com/snyk/actions/tree/master/golang

.github/workflows/snyk.yml

@@ -0,0 +1,18 @@
+name: Code Scanning with Snyk
+on: push
+jobs:
+  security:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Run Snyk to check for vulnerabilities
+        uses: snyk/actions/golang@master
+        continue-on-error: true # To make sure that SARIF upload gets called
+        env:
+          SNYK_TOKEN: ${{ secrets.SNYK_TOKEN }}
+        with:
+          args: --sarif-file-output=snyk.sarif
+      - name: Upload result to GitHub Code Scanning
+        uses: github/codeql-action/upload-sarif@v2
+        with:
+          sarif_file: snyk.sarif