Update CI

Author: takikawa

.github/workflows/ci.yml

@@ -26,6 +26,6 @@ jobs:
       - uses: actions/checkout@v4
       - name: Install Racket
         run: sudo apt-get install -y racket
-      - name: Run a multi-line script
+      - name: Run unit tests
         run: |
-          cd $GITHUB_WORKSPACE && raco test
+          racket $GITHUB_WORKSPACE/tests/unit-tests.rkt