remove unconditional mpi4py build

.github/workflows/nestbuildmatrix.yml

@@ -563,19 +563,16 @@ jobs:
 
       - name: "Install Linux system dependencies"
         run: |
-          sudo apt-get update
           # https://github.com/actions/virtual-environments/blob/main/images/linux/Ubuntu2004-README.md
+          sudo apt-get update
           sudo apt-get install \
                            ccache \
-                           python3-all-dev jq libpcre3 libpcre3-dev \
+                           python3-all-dev \
+                           jq \
+                           libpcre3 libpcre3-dev \
                            pkg-config
-
           # not sure why these would be required:
           #   sudo apt-get install tcl8.6 tcl8.6-dev tk8.6-dev
-          
-          # Install MPI dependencies regardless of whether we compile NEST with or without MPI, so the installation of MPI4Py works
-          sudo apt-get install openmpi-bin
-
           sudo ldconfig
 
       - name: "Install Readline dependencies"
@@ -592,7 +589,7 @@ jobs:
 
       - name: "Install OpenMPI development dependencies"
         if: "${{ contains(matrix.use, 'mpi') }}"
-        run: "sudo apt-get install libopenmpi-dev"
+        run: "sudo apt-get install openmpi-bin libopenmpi-dev"
 
       - name: "Install GSL system dependencies"
         if: "${{ contains(matrix.use, 'gsl') }}"
@@ -635,14 +632,24 @@ jobs:
 
       - name: "Install Python dependencies"
         run: |
-          python -m pip install --upgrade pip setuptools
+          python -m pip install --upgrade pip setuptools cython
           python -c "import setuptools; print('package location:', setuptools.__file__)"
-          python -m pip install --force-reinstall --upgrade scipy 'junitparser>=2' numpy pytest pytest-timeout pytest-xdist cython matplotlib terminaltables pandoc pandas
-          # Install mpi4py regardless of whether we compile NEST with or without MPI, so regressiontests/issue-1703.py will run in both cases
-          python -m pip install --force-reinstall --upgrade mpi4py
+          pip list
+
+      - name: "Install Python test dependencies" 
+        # These could go to a separate venv…
+        run: |
+          python -m pip install 'junitparser>=2' pytest pytest-timeout pytest-xdist terminaltables 
+          python -m pip install numpy scipy pandas matplotlib
           test \! -e "=2"   # assert junitparser is correctly quoted and '>' is not interpreted as shell redirect
           python -c "import pytest; print('package location:', pytest.__file__)"
-          pip list
+
+      - name: "Install Python doc dependencies"
+        run: "python -m pip install pandoc"
+
+      - name: "Install Python mpi dependencies" 
+        if: "${{ contains(matrix.use, 'mpi') }}"
+        run: "python -m pip install --force-reinstall --upgrade mpi4py"
 
       - name: "Install h5py"
         if: "${{ contains(matrix.use, 'hdf5') }}"