Add Gitea tips and tricks for TAs

Gitea-tips-and-tricks-for-TAs.md

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+
+## lfs and gitea actions
+
+bug: https://github.com/actions/checkout/issues/1830#issuecomment-2314758792
+
+solution: checkout lfs object separately 
+
+```yaml
+name: Run JOJ3 on Push
+on: [push]
+
+jobs:
+  run:
+    container:
+      image: focs.ji.sjtu.edu.cn:5000/gitea/runner-images:focs-ubuntu-latest-slim
+      volumes:
+        - /home/tt/.config:/home/tt/.config
+        - /home/tt/.cache:/home/tt/.cache
+        - /home/tt/.ssh:/home/tt/.ssh
+    steps:
+      - name: Check out repository code
+        uses: https://gitea.com/BoYanZh/checkout@focs
+        with:
+          fetch-depth: 0
+          lfs: false
+          persist-credentials: 'true'
+      - name: Checkout lfs
+        run: |
+          git lfs install --local
+          AUTH=$(git config --local http.https://focs.ji.sjtu.edu.cn/.extraheader)
+          git config --local --unset http.https://focs.ji.sjtu.edu.cn/.extraheader
+          git config --local http.${{ github.server_url }}/${{ github.repository }}.git/info/lfs/objects/batch.extraheader "$AUTH"
+          git lfs pull
+      - name: run joj3
+        run: |
+          sudo -E -u tt joj3 -conf-root /home/tt/.config/joj
+```