try fix dj prerelease lock

Author: bckohan

.github/workflows/test.yml

@@ -334,7 +334,8 @@ jobs:
         shell: bash
         run: |
           just setup ${{ steps.sp.outputs.python-path }}
-          if [[ "${{ matrix.django-version }}" =~ (a|b|rc) ]]; then
+          DJANGO_VERSION="${{ matrix.django-version }}"
+          if [[ "$DJANGO_VERSION" =~ (a|b|rc) ]]; then
             # prerelease, use exact version pin
             just test-lock Django==${{ matrix.django-version }}
           else