Fix CI Django version specifier to pin to intended minor version

The ~= specifier (e.g. ~=5.0) means >=5.0,==5.*, which installs the
latest 5.x release rather than the intended 5.0.x. Change to
>=X.Y.dev0,==X.Y.* to correctly pin each matrix entry to its minor
version while still allowing pre-releases.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mfogel

.github/workflows/ci.yml

@@ -150,7 +150,7 @@ jobs:
         if: steps.cached-poetry-dependencies.outputs.cache-hit != 'true'
         run: |
           source .venv/bin/activate
-          pip install --pre "Django~=${{ matrix.django-version }}"
+          pip install --pre "Django>=${{ matrix.django-version }}.dev0,==${{ matrix.django-version }}.*"
 
       - name: Install pytz
         if: steps.cached-poetry-dependencies.outputs.cache-hit != 'true' && matrix.tz-engine == 'pytz'