FEniCS adapter: Enable global venv again

It seems to be installing in `./venv/` by default.

Author: MakisH

tools/tests/dockerfiles/ubuntu_2404/Dockerfile

@@ -122,7 +122,8 @@ RUN add-apt-repository -y ppa:fenics-packages/fenics && \
 USER precice
 ARG FENICS_ADAPTER_REF
 # Building fenics-adapter
-RUN pip3 install git+https://github.com/precice/fenics-adapter.git@${FENICS_ADAPTER_REF}
+RUN . /home/precice/venv/bin/activate && \
+    pip3 install git+https://github.com/precice/fenics-adapter.git@${FENICS_ADAPTER_REF}
 
 
 FROM python_bindings AS nutils_adapter