fix: use manual git checkout instead of actions/checkout for Gitea compatibility

.gitea/workflows/syntax-check.yml

@@ -19,10 +19,12 @@ on:
 
 jobs:
   syntax-check:
-    runs-on: ubuntu-latest
+    runs-on: linux,x86_64,docker
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        run: |
+          git clone --depth 1 "$(echo "${{ gitea.server_url }}" | sed "s|://|://oauth2:${{ gitea.token }}@|")/${{ gitea.repository }}.git" .
+          git checkout -q ${{ github.sha }}
 
       - name: Install shellcheck
         run: sudo apt-get update && sudo apt-get install -y shellcheck