gh-128201: Fix DeprecationWarning in test_pdb (#128202)

Author: Eclips4

Lib/test/test_pdb.py

@@ -2065,10 +2065,7 @@ def test_pdb_next_command_for_coroutine():
         ...     await test_coro()
 
         >>> def test_function():
-        ...     loop = asyncio.new_event_loop()
-        ...     loop.run_until_complete(test_main())
-        ...     loop.close()
-        ...     asyncio.set_event_loop_policy(None)
+        ...     asyncio.run(test_main())
         ...     print("finished")
 
         >>> with PdbTestInput(['step',
@@ -2129,10 +2126,7 @@ def test_pdb_next_command_for_asyncgen():
         ...     await test_coro()
 
         >>> def test_function():
-        ...     loop = asyncio.new_event_loop()
-        ...     loop.run_until_complete(test_main())
-        ...     loop.close()
-        ...     asyncio._set_event_loop_policy(None)
+        ...     asyncio.run(test_main())
         ...     print("finished")
 
         >>> with PdbTestInput(['step',
@@ -2250,10 +2244,7 @@ def test_pdb_return_command_for_coroutine():
         ...     await test_coro()
 
         >>> def test_function():
-        ...     loop = asyncio.new_event_loop()
-        ...     loop.run_until_complete(test_main())
-        ...     loop.close()
-        ...     asyncio._set_event_loop_policy(None)
+        ...     asyncio.run(test_main())
         ...     print("finished")
 
         >>> with PdbTestInput(['step',
@@ -2350,10 +2341,7 @@ def test_pdb_until_command_for_coroutine():
         ...     await test_coro()
 
         >>> def test_function():
-        ...     loop = asyncio.new_event_loop()
-        ...     loop.run_until_complete(test_main())
-        ...     loop.close()
-        ...     asyncio._set_event_loop_policy(None)
+        ...     asyncio.run(test_main())
         ...     print("finished")
 
         >>> with PdbTestInput(['step',