Changed _matrix_power_symbolic function to condier mk=0 case

This fixes sagemath#36838. Here, I have added a condition to check whether
mk=0 or not. Because whenever mk=0 we should give mk^(n-i) (i.e. 0^(n-i))
instead of only 0 considering (n-i) can be equal to zero and in this
case 0^(n-i) will be more accurate than only 0.

src/sage/matrix/matrix2.pyx

@@ -18656,8 +18656,14 @@ def _matrix_power_symbolic(A, n):
         # D^i(f) / i! with f = x^n and D = differentiation wrt x
         if hasattr(mk, 'radical_expression'):
             mk = mk.radical_expression()
-        vk = [(binomial(n, i) * mk**(n-i)).simplify_full()
-              for i in range(nk)]
+
+        # Return mk^(n-i) instead of mk**(n-i) if mk=0
+        if mk:
+            vk = [(binomial(n, i) * mk**(n-i)).simplify_full()
+                  for i in range(nk)]
+        else:
+            vk = [(binomial(n, i)).simplify_full() * (mk^(n-i))
+                  for i in range(nk)] 
 
         # Form block Mk and insert it in M
         Mk = matrix(SR, [[SR.zero()]*i + vk[:nk-i] for i in range(nk)])