ci: manueller checkout statt actions/checkout

actions/checkout@v4 ist eine node-action; python:3.12-slim hat kein node
installiert -> 'exec: node not found'. ersatz durch git clone analog
release.yml.

.gitea/workflows/ci.yml

@@ -14,8 +14,16 @@ jobs:
     container:
       image: python:3.12-slim
     steps:
+      - name: Install git
+        run: |
+          apt-get update
+          apt-get install -y --no-install-recommends git ca-certificates
+          rm -rf /var/lib/apt/lists/*
+
       - name: Checkout
-        uses: actions/checkout@v4
+        run: |
+          git clone "${{ gitea.server_url }}/${{ gitea.repository }}.git" .
+          git checkout "${{ gitea.sha }}"
 
       - name: Install uv
         run: pip install --no-cache-dir uv