ci(coverage): install dev requirements on the KVM runner

The self-hosted KVM runner is a persistent machine, so
--break-system-packages is inappropriate. Use --user instead so
coverage (and pyright/pylint for future jobs) land in ~/.local
and survive between runs without touching the system Python.

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

.gitea/workflows/test.yml

@@ -103,6 +103,9 @@ jobs:
           # range overlap; it prints the exact `backend setup` fix.
           python3 cli.py backend status --backend=firecracker
 
+      - name: Install dev requirements
+        run: python3 -m pip install --user -r requirements-dev.txt
+
       - name: Combined coverage (unit + integration, incl. firecracker)
         run: PYTHON=python3 bash scripts/coverage.sh critical