tracemalloc: Add new functions from Python 3.9 (#4593)

Add tracemalloc.reset_peak()

stdlib/3/_tracemalloc.pyi

@@ -1,3 +1,4 @@
+import sys
 from tracemalloc import _FrameTupleT, _TraceTupleT
 from typing import Optional, Sequence, Tuple
 
@@ -8,5 +9,9 @@ def get_traceback_limit() -> int: ...
 def get_traced_memory() -> Tuple[int, int]: ...
 def get_tracemalloc_memory() -> int: ...
 def is_tracing() -> bool: ...
+
+if sys.version_info >= (3, 9):
+    def reset_peak() -> None: ...
+
 def start(__nframe: int = ...) -> None: ...
 def stop() -> None: ...