Revert "修正环境变量"

This reverts commit e10cd52.

Author: ZCShou

.github/workflows/test-qemu.yml

@@ -58,7 +58,6 @@ jobs:
 
       - name: Run tests
         run: |
-          export ROOTFS_DIR="${{ env.ROOTFS_DIR }}"
           export RUST_LOG=debug
           cargo xtask qemu \
             --build-config configs/board/qemu-${{ matrix.arch }}.toml \