ci: run Python job in python3.12+node container

setup-python@v5 can't fetch CPython 3.12 on the self-hosted Gitea runner
(it queries the Gitea API for actions/python-versions, which 404s), so the
job silently fell back to the image's system Python 3.10 + pip 22.0.2. That
old pip lacks PEP 660 editable support, so 'pip install -e' failed with
'build backend is missing the build_editable hook', and 3.10 is below the
project's requires-python>=3.11 (code uses datetime.UTC).

Run the job inside nikolaik/python-nodejs:python3.12-nodejs20 which bundles
Python 3.12, Node 20 (for actions/checkout) and modern pip, removing the
GitHub download dependency entirely.

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

.github/workflows/ci.yml

@@ -44,14 +44,13 @@ jobs:
   python:
     name: Python (ingestion)
     runs-on: ubuntu-latest
+    container:
+      image: nikolaik/python-nodejs:python3.12-nodejs20
     defaults:
       run:
         working-directory: ingestion
     steps:
       - uses: actions/checkout@v4
-      - uses: actions/setup-python@v5
-        with:
-          python-version: "3.12"
       - name: Install
         run: pip install -e ".[dev]"
       - name: Ruff lint