Use more reasonable nesting in test_plistlib's test_deep_nesting

This adjust the nesting levels used by the test_deep_nesting
because the previous levels consistently hit the recursion limit
and ended up not testing anything.

Adjusting the level is reasonable because the tested nesting levels
should still be significantly larger than those seen in real world
plist files.

The test also no longer ignores recursion errors.

Lib/test/test_plistlib.py

@@ -971,18 +971,15 @@ def test_cycles(self):
         self.assertIs(b['x'], b)
 
     def test_deep_nesting(self):
-        for N in [300, 100000]:
+        for N in [50, 100]:
+          with self.subTest(N=N):
             chunks = [b'\xa1' + (i + 1).to_bytes(4, 'big') for i in range(N)]
-            try:
-                result = self.decode(*chunks, b'\x54seed', offset_size=4, ref_size=4)
-            except RecursionError:
-                pass
-            else:
-                for i in range(N):
-                    self.assertIsInstance(result, list)
-                    self.assertEqual(len(result), 1)
-                    result = result[0]
-                self.assertEqual(result, 'seed')
+            result = self.decode(*chunks, b'\x54seed', offset_size=4, ref_size=4)
+            for i in range(N):
+                self.assertIsInstance(result, list)
+                self.assertEqual(len(result), 1)
+                result = result[0]
+            self.assertEqual(result, 'seed')
 
     def test_large_timestamp(self):
         # Issue #26709: 32-bit timestamp out of range