Update the doc to use breakpoint() (#20691)

According to my friend ChatGPT, using pdb.set_trace() is too old-school. Update the doc to use breakpoint() instead to stay young 😎

Author: briannnyee

docs/source-pytorch/debug/debugging_basic.rst

@@ -33,9 +33,7 @@ A breakpoint stops your code execution so you can inspect variables, etc... and
         x = 2
 
         # set breakpoint
-        import pdb
-
-        pdb.set_trace()
+        breakpoint()
         y = x**2
 
 In this example, the code will stop before executing the ``y = x**2`` line.