Fix CI: use git checkout without node actions

.forgejo/workflows/ci.yml

@@ -14,7 +14,17 @@ jobs:
     container:
       image: gradle:8.7-jdk21
     steps:
-      - uses: actions/checkout@v3
+      - name: Install git
+        run: |
+          apt-get update
+          apt-get install -y --no-install-recommends git ca-certificates
+          git --version
+
+      - name: Checkout (git)
+        run: |
+          git clone "${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}" .
+          git checkout "${GITHUB_SHA}"
+
       - name: Test + build (backend)
         working-directory: back001
         run: ./gradlew test build --no-daemon
@@ -24,7 +34,17 @@ jobs:
     container:
       image: ghcr.io/cirruslabs/flutter:stable
     steps:
-      - uses: actions/checkout@v3
+      - name: Install git
+        run: |
+          apt-get update
+          apt-get install -y --no-install-recommends git ca-certificates
+          git --version
+
+      - name: Checkout (git)
+        run: |
+          git clone "${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}" .
+          git checkout "${GITHUB_SHA}"
+
       - name: Analyze + test (flutter)
         working-directory: front001/mosenioring
         run: |