MAINT: Added conditionals to install openmpi according to matrix.os

.github/workflows/unit_tests.yml

@@ -23,19 +23,19 @@ jobs:
         with:    
           python-version: ${{ matrix.python-version }}
       - name: Install ubuntu dependencies
+        if: contains(matrix.os, 'ubuntu')
         shell: bash -el {0}
         run: |
-          if [ "${{ matrix.os }}" == "ubuntu-latest" ]; then
             sudo add-apt-repository ppa:ubuntu-toolchain-r/test
             sudo apt-get update
             sudo apt-get install libopenmpi-dev openmpi-bin
-          fi;
+
       - name: Install MacOs dependencies
+        if: contains(matrix.os, 'macos')
         shell: bash -el {0}
         run: |
-          if [ "${{ matrix.os }}" == "macos-latest" ]; then
               brew install open-mpi
-          fi;
+
       - name: Install dependencies
         shell: bash -el {0}
         run: |