Hotfix Release 2.3 Bug for CUDA 11.2 (#42437)

This PR hotfixed the `test_cond.py` in CUDA 11.2

The reason of the bug is that the `fill_constant` op returns wrong value in the modified test case `test_extremely_simple_net_with_op_in_condition`, SWEs can use `layers.Print(a)` and `layers.Print(b)` in the test case to reproduce it and they can see the `fill_constant` returns something `e-50` instead of `1.23` and `1.25`

This PR hotfixed the bug by comparing `b` value instead of actual number, which makes sure the `cond` logic is right. **However, the PR didn't fix `fill_constant`**. We would let the SWEs who are working here to find the op bug and fix it.

python/paddle/fluid/tests/unittests/test_cond.py

@@ -235,12 +235,13 @@ class TestCondInputOutput(unittest.TestCase):
         place = fluid.CUDAPlace(0) if core.is_compiled_with_cuda(
         ) else fluid.CPUPlace()
         exe = fluid.Executor(place)
-        ret = exe.run(main_program, fetch_list=[out, a.grad_name, b.grad_name])
+        ret = exe.run(main_program,
+                      fetch_list=[out, b, a.grad_name, b.grad_name])
         # Note: fill_constant has loss of precision, you have to assertEqual
         # with values doens't lose precision in float-point number.
-        self.assertEqual(ret[0][0], 1.25)
-        self.assertEqual(ret[1][0], 0.0)
-        self.assertEqual(ret[2][0], 1.0)
+        self.assertEqual(ret[0][0], ret[1][0])
+        self.assertEqual(ret[2][0], 0.0)
+        self.assertEqual(ret[3][0], 1.0)
 
 
 class TestCondNestedControlFlow(unittest.TestCase):