Revert "Use parent directory for backend"

This reverts commit b003e8e.

Author: MikuroXina

.github/workflows/ci.yaml

@@ -40,10 +40,10 @@ jobs:
         uses: actions/checkout@v6
         with:
           repository: "pulsate-dev/pulsate"
-          path: "../backend/"
+          path: "backend/"
 
       - name: Build backend
-        working-directory: "../backend"
+        working-directory: "./backend"
         run: |
           pnpm install --frozen-lockfile
           pnpm run build
@@ -55,6 +55,6 @@ jobs:
         run: |
           set -e
           pnpm playwright install chromium --only-shell
-          cd ../backend && pnpm start & id=$!
+          cd backend && pnpm start & id=$!
           pnpm e2e
           kill "$id"