ci: drop actions/setup-python from the remaining workflows

Applies the same fix as test/lint to every workflow that still used
actions/setup-python, which the old act_runner engine mishandles:

- update-badges: was broken identically to lint — setup-python + pip
  install hit the image's externally-managed system Python. Drop
  setup-python, install with --break-system-packages, and use `python3`
  (not bare `python`) for the coverage steps.
- canaries, prd-number: no pip install, so not failing, but they carried
  the same fragile (and network-heavy) setup-python for stdlib-only work.
  Removed — the image's system Python 3.12 runs them directly.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UoEZHDjv84ChoZbozQERhJ

.gitea/workflows/canaries.yml

@@ -22,10 +22,7 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Set up Python
-        uses: actions/setup-python@v5
-        with:
-          python-version: "3.12"
-
+      # No actions/setup-python: canaries are stdlib unittest on the image's
+      # system Python 3.12 (older act_runner mishandles setup-python's PATH).
       - name: Run canaries
         run: python3 -m unittest discover -t . -s tests/canaries -v

.gitea/workflows/prd-number.yml

@@ -37,11 +37,8 @@ jobs:
           fetch-depth: 0
           token: ${{ secrets.GITHUB_TOKEN }}
 
-      - name: Set up Python
-        uses: actions/setup-python@v5
-        with:
-          python-version: "3.12"
-
+      # No actions/setup-python: the inline script is stdlib-only on the
+      # image's system Python 3.12 (older act_runner mishandles its PATH).
       - name: Configure git
         run: |
           git config user.name "github-actions[bot]"

.gitea/workflows/update-badges.yml

@@ -20,21 +20,18 @@ jobs:
           fetch-depth: 0
           token: ${{ secrets.GITHUB_TOKEN }}
 
-      - name: Set up Python
-        uses: actions/setup-python@v4
-        with:
-          python-version: '3.12'
-
+      # No actions/setup-python: the runner image ships Python 3.12 and older
+      # act_runner engines mishandle setup-python's PATH. Install into the
+      # ephemeral job container's system Python (--break-system-packages is
+      # safe because the container is disposable).
       - name: Install dev dependencies
-        run: |
-          python -m pip install --upgrade pip
-          pip install -r requirements-dev.txt
+        run: python3 -m pip install --break-system-packages -r requirements-dev.txt
 
       - name: Run coverage and extract percentage
         id: coverage
         run: |
-          python -m coverage run -m unittest discover -t . -s tests/unit > /dev/null 2>&1 || true
-          PERCENT=$(python -m coverage report 2>/dev/null | grep '^TOTAL' | grep -oP '\d+(?=%)' | tail -1)
+          python3 -m coverage run -m unittest discover -t . -s tests/unit > /dev/null 2>&1 || true
+          PERCENT=$(python3 -m coverage report 2>/dev/null | grep '^TOTAL' | grep -oP '\d+(?=%)' | tail -1)
           echo "percent=$PERCENT" >> $GITHUB_OUTPUT
           echo "Coverage: $PERCENT%"
 
@@ -45,7 +42,7 @@ jobs:
           # the single source of truth in scripts/critical-modules.txt; every
           # core module is unit-tested, so the unit-only run is accurate for it.
           INCLUDE=$(grep -vE '^[[:space:]]*(#|$)' scripts/critical-modules.txt | paste -sd, -)
-          PERCENT=$(python -m coverage report --include="$INCLUDE" 2>/dev/null | grep '^TOTAL' | grep -oP '\d+(?=%)' | tail -1)
+          PERCENT=$(python3 -m coverage report --include="$INCLUDE" 2>/dev/null | grep '^TOTAL' | grep -oP '\d+(?=%)' | tail -1)
           echo "percent=$PERCENT" >> $GITHUB_OUTPUT
           echo "Core coverage: $PERCENT%"