ci: use local Docker backend instead of Modal for CI tests

Modal requires authentication tokens that aren't available to fork PRs.
Using the local Docker backend allows CI to run without Modal credentials.

Co-authored-by: openhands <openhands@all-hands.dev>

Author: openhands-agent

.github/workflows/system.yml

@@ -25,19 +25,13 @@ jobs:
       - name: Get tests
         run: uv run commit0 get-tests simpy
       - name: Test
-        env:
-          MODAL_TOKEN_ID: ${{secrets.MODAL_TOKEN_ID}}
-          MODAL_TOKEN_SECRET: ${{secrets.MODAL_TOKEN_SECRET}}
         run: |
-          uv run commit0 test simpy tests/test_event.py::test_succeed --reference --rebuild
-          uv run commit0 test simpy tests/test_event.py::test_succeed --reference
+          uv run commit0 test simpy tests/test_event.py::test_succeed --reference --rebuild --backend local
+          uv run commit0 test simpy tests/test_event.py::test_succeed --reference --backend local
       - name: Evaluate
-        env:
-          MODAL_TOKEN_ID: ${{secrets.MODAL_TOKEN_ID}}
-          MODAL_TOKEN_SECRET: ${{secrets.MODAL_TOKEN_SECRET}}
         run: |
-          uv run commit0 evaluate --reference  --rebuild
-          uv run commit0 evaluate --reference
+          uv run commit0 evaluate --reference  --rebuild --backend local
+          uv run commit0 evaluate --reference --backend local
       - name: Lint
         run: uv run commit0 lint commit0/harness/
       - name: Save