update syntax

Author: parthea

.github/workflows/tests.yaml

@@ -394,10 +394,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - name: Set up Python ${PRERELEASE_PYTHON}
+      - name: Set up Python ${{ vars.PRERELEASE_PYTHON }}
         uses: actions/setup-python@v5
         with:
-          python-version: ${PRERELEASE_PYTHON}
+          python-version: ${{ vars.PRERELEASE_PYTHON }}
           cache: 'pip'
       - name: Install nox.
         run: |