ci: single molecule job running all pairs in parallel

Gitea Actions does not honor fail-fast/max-parallel for cancelling
other matrix runners when one fails. Use a single molecule job that
runs all (scenario, platform) pairs via run_molecule_parallel.py.
This gives true parallel execution + immediate termination on the
first failure, which is what we need to debug efficiently.

Generated with [Devin](https://devin.ai)

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

.gitea/workflows/ci.yml

@@ -29,24 +29,16 @@ jobs:
   molecule-tests:
     needs: quality
     runs-on: docker
-    strategy:
-      fail-fast: true
-      matrix:
-        runner-index: [0, 1, 2]
     steps:
       - uses: actions/checkout@v4
       - name: Set up environment
         run: make setup
-      - name: Discover assigned test pairs
-        run: |
-          . .venv/bin/activate
-          PAIRS=$(python3 scripts/distribute_molecule.py --runner-index ${{ matrix.runner-index }} --max-runners 3)
-          echo "Assigned pairs: $PAIRS"
-          echo "TEST_PAIRS=$PAIRS" >> $GITHUB_ENV
-      - name: Run molecule tests
+      - name: Run all molecule tests in parallel
         run: |
           set -euo pipefail
           . .venv/bin/activate
           export DOCKER_HOST="unix:///run/user/$(id -u)/docker.sock"
           export ANSIBLE_INJECT_INVOCATION=1
-          python3 scripts/run_molecule_parallel.py $TEST_PAIRS
+          PAIRS=$(python3 scripts/distribute_molecule.py --runner-index 0 --max-runners 1)
+          echo "Running all pairs in parallel: $PAIRS"
+          python3 scripts/run_molecule_parallel.py $PAIRS