ci: remove GitHub-hosted actions, manual checkout + Go from CN mirror

Self-hosted Gitea runner has flaky/blocked access to github.com, causing
actions/checkout and actions/setup-go to time out intermittently across all
jobs. Replace them with:
- manual git checkout against $GITHUB_SERVER_URL (the Gitea host, reachable
  from job containers)
- Go installed from mirrors.aliyun.com

Python job stays on the python3.12-nodejs20 container (fixes the original
PEP 660 editable-install failure). No more github.com network dependency.

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

.github/workflows/ci.yml

@@ -5,6 +5,10 @@ on:
     branches: [main]
   pull_request:
 
+env:
+  GO_VERSION: "1.23.12"
+  GOPROXY: "https://goproxy.cn,direct"
+
 jobs:
   go:
     name: Go (api)
@@ -25,11 +29,22 @@ jobs:
     env:
       OPENGOODS_DATABASE_URL: postgres://opengoods:opengoods@postgres:5432/opengoods?sslmode=disable
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-go@v5
-        with:
-          go-version: "1.23"
-          cache-dependency-path: api/go.sum
+      - name: Checkout
+        working-directory: ${{ github.workspace }}
+        run: |
+          git config --global --add safe.directory '*'
+          git init -q .
+          git remote add origin "${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}.git"
+          git -c protocol.version=2 fetch -q --no-tags --depth 1 origin "${GITHUB_REF}"
+          git checkout -q --force FETCH_HEAD
+      - name: Setup Go
+        working-directory: ${{ github.workspace }}
+        run: |
+          curl -fsSL -o /tmp/go.tgz "https://mirrors.aliyun.com/golang/go${GO_VERSION}.linux-amd64.tar.gz"
+          rm -rf /usr/local/go
+          tar -C /usr/local -xzf /tmp/go.tgz
+          echo "/usr/local/go/bin" >> "$GITHUB_PATH"
+          echo "$HOME/go/bin" >> "$GITHUB_PATH"
       - name: Apply migrations
         working-directory: .
         run: |
@@ -50,7 +65,14 @@ jobs:
       run:
         working-directory: ingestion
     steps:
-      - uses: actions/checkout@v4
+      - name: Checkout
+        working-directory: ${{ github.workspace }}
+        run: |
+          git config --global --add safe.directory '*'
+          git init -q .
+          git remote add origin "${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}.git"
+          git -c protocol.version=2 fetch -q --no-tags --depth 1 origin "${GITHUB_REF}"
+          git checkout -q --force FETCH_HEAD
       - name: Install
         run: pip install -e ".[dev]"
       - name: Ruff lint
@@ -76,10 +98,21 @@ jobs:
     env:
       DBURL: postgres://opengoods:opengoods@postgres:5432/opengoods?sslmode=disable
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-go@v5
-        with:
-          go-version: "1.23"
+      - name: Checkout
+        working-directory: ${{ github.workspace }}
+        run: |
+          git config --global --add safe.directory '*'
+          git init -q .
+          git remote add origin "${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}.git"
+          git -c protocol.version=2 fetch -q --no-tags --depth 1 origin "${GITHUB_REF}"
+          git checkout -q --force FETCH_HEAD
+      - name: Setup Go
+        run: |
+          curl -fsSL -o /tmp/go.tgz "https://mirrors.aliyun.com/golang/go${GO_VERSION}.linux-amd64.tar.gz"
+          rm -rf /usr/local/go
+          tar -C /usr/local -xzf /tmp/go.tgz
+          echo "/usr/local/go/bin" >> "$GITHUB_PATH"
+          echo "$HOME/go/bin" >> "$GITHUB_PATH"
       - name: Install golang-migrate
         run: go install -tags 'postgres' github.com/golang-migrate/migrate/v4/cmd/migrate@v4.18.1
       - name: Migrate up