Skip Jacobian matrix tests in macOS parallel tests CI job

This test is extremely slow when run in parallel on macOS (maybe the
macOS servers on Github Actions don't have enough memory?), so skip it
in this case to avoid test failures.

moment_kinetics/test/jacobian_matrix_tests.jl

@@ -10,6 +10,7 @@ using moment_kinetics.array_allocation: allocate_shared_float
 using moment_kinetics.boundary_conditions: enforce_v_boundary_condition_local!,
                                            enforce_vperp_boundary_condition!
 using moment_kinetics.calculus: derivative!
+using moment_kinetics.communication
 using moment_kinetics.derivatives: derivative_z!, derivative_z_pdf_vpavperpz!
 using moment_kinetics.electron_fluid_equations: calculate_electron_qpar_from_pdf_no_r!,
                                                 electron_energy_equation_no_r!,
@@ -3534,6 +3535,11 @@ function test_electron_kinetic_equation(test_input; rtol=(5.0e2*epsilon)^2)
 end
 
 function runtests()
+    if Sys.isapple() && "CI" ∈ keys(ENV) && global_size[] > 1
+        # These tests are too slow in the parallel tests job on macOS, so skip in that
+        # case.
+        return nothing
+    end
     # Create a temporary directory for test output
     test_output_directory = get_MPI_tempdir()
     test_input["output"]["base_directory"] = test_output_directory