ci: add postgres service for procrastinate integration tests

The integration_tests.yml workflow only provisioned Redis (for Celery),
so the procrastinate tests added in #46 failed on every push to main
with `psycopg_pool.PoolTimeout`. Adds a postgres:16 service container
matching the DSN the tests default to, and sets PROCRASTINATE_DSN
explicitly so the test config is self-documenting.

Also picks up the uv.lock entry for taskbadger 2.1.0a1 that should
have ridden along with #47.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: snopoke

.github/workflows/integration_tests.yml

@@ -17,6 +17,19 @@ jobs:
           --health-retries 5
         ports:
           - 6379:6379
+      postgres:
+        image: postgres:16
+        env:
+          POSTGRES_USER: postgres
+          POSTGRES_PASSWORD: postgres
+          POSTGRES_DB: procrastinate
+        options: >-
+          --health-cmd "pg_isready -U postgres"
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
+        ports:
+          - 5432:5432
     steps:
       - uses: actions/checkout@v6
       - name: Set up Python
@@ -36,3 +49,4 @@ jobs:
           TASKBADGER_ORG: ${{ vars.TASKBADGER_ORG }}
           TASKBADGER_PROJECT: ${{ vars.TASKBADGER_PROJECT }}
           TASKBADGER_API_KEY: ${{ secrets.TASKBADGER_API_KEY }}
+          PROCRASTINATE_DSN: postgresql://postgres:postgres@localhost:5432/procrastinate