GH-102341: Improve the test function for pow (GH-102342)

(cherry picked from commit 3222054)

Co-authored-by: Partha P. Mukherjee <ppm.floss@gmail.com>
Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Lib/test/test_pow.py

@@ -19,12 +19,11 @@ def powtest(self, type):
                 self.assertEqual(pow(2, i), pow2)
                 if i != 30 : pow2 = pow2*2
 
-            for othertype in (int,):
-                for i in list(range(-10, 0)) + list(range(1, 10)):
-                    ii = type(i)
-                    for j in range(1, 11):
-                        jj = -othertype(j)
-                        pow(ii, jj)
+            for i in list(range(-10, 0)) + list(range(1, 10)):
+                ii = type(i)
+                inv = pow(ii, -1) # inverse of ii
+                for jj in range(-10, 0):
+                    self.assertAlmostEqual(pow(ii, jj), pow(inv, -jj))
 
         for othertype in int, float:
             for i in range(1, 100):