Temporarily exclude fusion rewrite from Numba Scan tests

Otherwise they fail due to lack of support for multi-output Elemwises in the Numba backend

tests/link/numba/test_scan.py

@@ -367,6 +367,8 @@ def f_pow2(x_tm2, x_tm1):
     state_val = np.array([1.0, 2.0])
 
     numba_mode = get_mode("NUMBA").including("scan_save_mem")
+    # multi-output Elemwise not supported in NUMBA
+    numba_mode = numba_mode.excluding("fusion")
     py_mode = Mode("py").including("scan_save_mem")
 
     out_fg = FunctionGraph([init_x, n_steps], [output])
@@ -406,6 +408,8 @@ def inner_fct(seq, state_old, state_current):
     g_outs = grad(out.sum(), [seq, init_x])
 
     numba_mode = get_mode("NUMBA").including("scan_save_mem")
+    # multi-output Elemwise not supported in NUMBA
+    numba_mode = numba_mode.excluding("fusion")
     py_mode = Mode("py").including("scan_save_mem")
 
     out_fg = FunctionGraph([seq, init_x], g_outs)