ci: replace checkout action with shell clone on Forgejo

Avoid JS-based checkout action dependency because runner image lacks node binary.

.forgejo/workflows/build_release.yml

@@ -18,9 +18,16 @@ jobs:
     runs-on: forgejo-release
     steps:
       - name: Clone repository
-        uses: actions/checkout@v4 # Forgejo-compatible (node20)
-        with:
-          fetch-depth: 0
+        shell: bash
+        env:
+          FORGEJO_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          set -euo pipefail
+          rm -rf .git
+          git init .
+          git remote add origin "http://copilot:${FORGEJO_TOKEN}@127.0.0.1:3030/${GITHUB_REPOSITORY}.git"
+          git fetch --tags --prune --depth=1 origin "${GITHUB_SHA}"
+          git checkout --force FETCH_HEAD
 
       - name: Set up JDK
         shell: bash