add new reftest for modal Bernstein formulation

test/IntegrationTests/refs/modal_bernstein_advection_sine/modal_bernstein_advection_sine.toml

+[Evolution]
+cfl = 0.5
+tend = 2.2
+
+[ScalarEq]
+analyze_error = false
+equation = "advection"
+id = "sine"
+
+[Output]
+substep_every_iteration = 200
+interpolate_variables = ["u"]
+substep_variables = ["u"]
+interpolate_aligned_ts = [0.3, 0.6, 0.8]
+aligned_ts = [0.05, 0.1, 0.15, 0.2]
+interpolate_nodes = "$(collect(range(0.0,1.0,length=10)))"
+variables1d = ["u"]
+
+[Mesh]
+dg_kind = "modal_bernstein"
+range = [0.0, 1.0]
+k = 40
+basis = "lgl"
+n = 4

test/IntegrationTests/refs/testconfig.toml

@@ -7,6 +7,9 @@ default_abstol1d = 1e-8
 [advection_sine]
 variables1d = [ "u", "u_err" ]
 
+[modal_bernstein_advection_sine]
+variables1d = [ "u" ]
+
 [advection_sine_analysis]
 variables0d = [ "u_err_norm", "u_norm2" ]
 variables1d = [ "u" ]