Try with old matrix for starters

Author: willend

.github/workflows/mcstas-conda-nightly.yml

@@ -16,13 +16,15 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - { os: ubuntu-latest }
-          - { os: ubuntu-24.04-arm }
-          - { os: macos-latest }
-          - { os: windows-latest }
-          - { os: windows-11-arm }
-  
-        - name: Setup python
+          - { os: ubuntu-latest, CC: clang,    CXX: clang++,    python: '3.12', mpi: 'openmpi' }
+          - { os: ubuntu-latest, CC: clang,    CXX: clang++,    python: '3.12', mpi: 'mpich' }
+          - { os: ubuntu-latest, CC: gcc,    CXX: g++,    python: '3.12', mpi: 'openmpi' }
+          - { os: ubuntu-latest, CC: gcc,    CXX: g++,    python: '3.12', mpi: 'mpich' }
+          #- { os: macos-latest, CC: clang,    CXX: clang++,    python: '3.12', mpi: 'openmpi' }
+          - { os: macos-latest, CC: clang,    CXX: clang++,    python: '3.12', mpi: 'mpich' }
+          - { os: windows-latest, CC: gcc,    CXX: g++,    python: '3.12', mpi: 'msmpi' }
+
+        - name: Setup mamba
           uses: mamba-org/setup-micromamba@v2
           with:
             environment-file: environment.yml