dealii, test for specific version

Specified that test case “step-40” is only to be run when using dealii
version 8.4.0 or later

var/spack/repos/builtin/packages/dealii/package.py

@@ -228,6 +228,7 @@ def install(self, spec, prefix):
 
         # take step-40 which can use both PETSc and Trilinos
         # FIXME: switch step-40 to MPI run
+        if spec.satisfies('@8.4.0:'):
             with working_dir('examples/step-40'):
                 print('=====================================')
                 print('========== Step-40 PETSc ============')