Revert "We shall try installin MPICH from Spack for now"

This reverts commit 33b847f.

Author: franzpoeschel

.github/ci/spack-envs/gcc13_py312_mpich_h5_ad2/spack.yaml

@@ -20,6 +20,11 @@ spack:
       buildable: False
     hdf5:
       variants: +mpi
+    mpich:
+      externals:
+      - spec: mpich@4.2.0
+        prefix: /usr
+      buildable: False
     perl:
       externals:
       - spec: perl@5.38.2

.github/workflows/linux.yml

@@ -172,20 +172,19 @@ jobs:
       run: |
         sudo apt-get update
         sudo apt-get remove openmpi* libopenmpi* *hdf5* || true
-        sudo apt-get install g++ gfortran python3
+        sudo apt-get install g++ gfortran libmpich-dev mpich python3
         sudo .github/workflows/dependencies/install_spack
     - name: Build
       env: {CC: gcc, CXX: g++, MPICH_CC: gcc, MPICH_CXX: g++, CXXFLAGS: -Werror}
       run: |
         cmake --version
+        mpiexec --version
+        mpicxx --version
         perl --version
         python --version
         eval $(spack env activate --sh .github/ci/spack-envs/gcc13_py312_mpich_h5_ad2/)
         spack install
 
-        mpiexec --version
-        mpicxx --version
-
         share/openPMD/download_samples.sh build
         cmake -S . -B build \
           -DopenPMD_USE_PYTHON=OFF \