fix: re-pin PySide6 after the beamline-plugin install in CI

The bec plugin editable installs upgrade PySide6 to 6.11.x past the
pyproject cap, which brings the teardown segfault back in exactly the
test-with-beamline-plugins jobs. Reinstall the capped version after
the plugin install.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -102,6 +102,10 @@ jobs:
           git clone https://gitea.psi.ch/bec/${{ matrix.plugin_repo }}.git
           uv pip install -e ./mx_bec
           uv pip install -e ./${{ matrix.plugin_repo }}
+          # The bec plugin deps drag PySide6 up to >=6.10, which segfaults
+          # the unit suite in teardown (see the pyproject pin). Force the
+          # project's capped version back after the plugin install.
+          uv pip install "pyside6<6.10"
 
       - name: Run Pytest
         env: