CI: Remove manual fortran installation in spack Linux build

Fortran is already installed in the ubuntu images on GitHub Actions.

Author: rbuch

.github/workflows/spack.yml

@@ -21,7 +21,6 @@ jobs:
         cd ..
         git clone --depth 1 https://github.com/spack/spack
         cd spack
-        [[ $(uname) == "Linux" ]] && sudo apt-get install -y gfortran gfortran-7 gfortran-8 gfortran-9 gfortran-10
 
         # Use this branch for testing, not main
         sed -i -e 's,="main",="${{ github.head_ref }}",' var/spack/repos/builtin/packages/charmpp/package.py