ci: create venv before using it

Author: JJTech0130

.github/workflows/python-package.yml

@@ -22,6 +22,7 @@ jobs:
     - uses: actions/checkout@v4
     - name: Activate virtualenv
       run: |
+        python -m venv .venv
         . .venv/bin/activate
         echo PATH=$PATH >> $GITHUB_ENV
     - name: Set up Python ${{ matrix.python-version }}