fix winpty env var name

Author: bckohan

.github/workflows/test.yml

@@ -131,7 +131,7 @@ jobs:
       COVERAGE_FILE: py${{ matrix.python-version }}-windows-dj${{ matrix.django-version }}.coverage
       TEST_PYTHON_VERSION: ${{ matrix.python-version }}
       TEST_DJANGO_VERSION: ${{ matrix.django-version }}
-      WINPTY_MSC: ${{ github.workspace }}\winpty-msvc
+      WINPTY_ROOT: ${{ github.workspace }}\winpty-msvc
     steps:
     - uses: actions/checkout@v5
       with: