Fix Python CI jobs: drop container, install Python 3.12 directly

python:3.12-slim has no Node, causing actions/checkout@v4's post-step
to fail with 'exec: node not found'. Drop the container: declaration
so jobs run on the ubuntu-latest runner (which has Node). Install
Python 3.12 via deadsnakes PPA for the test job since the runner base
image (Ubuntu 22.04) ships with Python 3.10.

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

.forgejo/workflows/ci.yml

@@ -60,8 +60,6 @@ jobs:
   lint:
     name: Python lint
     runs-on: ubuntu-latest
-    container:
-      image: python:3.12-slim
     steps:
       - uses: actions/checkout@v4
 
@@ -74,20 +72,25 @@ jobs:
   test:
     name: Python tests
     runs-on: ubuntu-latest
-    container:
-      image: python:3.12-slim
     steps:
       - uses: actions/checkout@v4
 
-      # git is required by setuptools-scm during package build
-      - name: Install git
-        run: apt-get update -qq && apt-get install -y -qq git
+      # The act runner base image ships Ubuntu 22.04 with Python 3.10.
+      # Our package requires 3.12, so install it from the deadsnakes PPA.
+      - name: Install Python 3.12
+        run: |
+          apt-get update -qq
+          apt-get install -y -qq software-properties-common
+          add-apt-repository -y ppa:deadsnakes/ppa
+          apt-get update -qq
+          apt-get install -y -qq python3.12 python3.12-dev python3.12-venv python3-pip git
+          python3.12 -m ensurepip --upgrade
 
       - name: Install package with dev deps
-        run: pip install -e ".[dev]"
+        run: python3.12 -m pip install -e ".[dev]"
 
       - name: Run tests
-        run: pytest tests/ -v
+        run: python3.12 -m pytest tests/ -v
 
   build:
     name: Build & push image