ci: replace actions/checkout with raw git clone

.gitea/workflows/ci.yaml

@@ -11,7 +11,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        run: |
+          git init
+          git remote add origin https://git.rua.plus/${{ github.repository }}.git
+          git fetch --depth 1 origin ${{ github.sha }}
+          git checkout ${{ github.sha }}
 
       - name: Install Rust toolchain
         run: |
@@ -49,7 +53,11 @@ jobs:
     needs: check
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        run: |
+          git init
+          git remote add origin https://git.rua.plus/${{ github.repository }}.git
+          git fetch --depth 1 origin ${{ github.sha }}
+          git checkout ${{ github.sha }}
 
       - name: Install Rust toolchain
         run: |