fix a CI error

.github/workflows/main.yml

@@ -17,7 +17,7 @@ jobs:
     - uses: actions/checkout@v3
     - uses: ilammy/msvc-dev-cmd@v1
     - name: Compile
-      shell: bash
+      shell: powershell
       run: |
         python3 amalgamate.py
         cd amalgamated