ci: fix unit-tests job on the Debian-packaged runner pip

The runner image ships pip 24.0 from the Debian package, so
`pip install --upgrade pip` aborts with "Cannot uninstall pip 24.0,
RECORD file not found" and the job failed after 4s. Drop the upgrade
and install with --break-system-packages.

.gitea/workflows/test.yml

@@ -16,9 +16,11 @@ jobs:
       - name: Install dependencies
         # Mirrors the Dockerfile: the container installs qbittorrent-api
         # unpinned, so requirements.txt is not used here.
+        # --break-system-packages: the runner image ships a Debian-packaged
+        # pip, so a plain install (or `pip install --upgrade pip`) fails
+        # with "RECORD file not found".
         run: |
-          python3 -m pip install --upgrade pip
-          python3 -m pip install requests qbittorrent-api coverage
+          python3 -m pip install --break-system-packages requests qbittorrent-api coverage
       - name: Run the full suite with coverage
         run: |
           python3 -m coverage run --rcfile=.coveragerc -m unittest \