ci(govulncheck): check out with plain git; the golang image has no node (M462 #4984)

actions/checkout runs on node, which golang:1.26-bookworm does not carry,
so the lane died at checkout (run 8272, exit 127) before scanning
anything. That run was also the gate's first red: every other lane
passed, and image-release and release-assets both skipped, leaving :dev
on the previous build.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/release.yml

@@ -383,8 +383,19 @@ jobs:
       image: golang:1.26-bookworm
 
     steps:
+      # Plain git, not actions/checkout: that action runs on node, which the
+      # golang image does not carry. This step is dash (rule 81).
       - name: Checkout
-        uses: actions/checkout@v4
+        env:
+          TOKEN: ${{ github.token }}
+        run: |
+          set -eu
+          auth=$(printf 'x-access-token:%s' "$TOKEN" | base64 -w0)
+          git init -q .
+          git remote add origin "${{ github.server_url }}/${{ github.repository }}.git"
+          git -c http.extraHeader="Authorization: Basic ${auth}" fetch -q --depth 1 origin "${{ github.sha }}"
+          git checkout -q FETCH_HEAD
+          git log -1 --format='%H %s'
 
       - name: govulncheck
         run: |