gh-158234: Fix a typo in the tracemalloc cumulative mode error message (#158233)

Co-authored-by: Stan Ulbrych <stan@python.org>

Author: Tony123-tech

Lib/tracemalloc.py

@@ -119,6 +119,7 @@ def _sort_key(self):
 
 def _compare_grouped_stats(old_group, new_group):
     statistics = []
+    old_group = dict(old_group)
     for traceback, stat in new_group.items():
         previous = old_group.pop(traceback, None)
         if previous is not None:
@@ -478,7 +479,7 @@ def _group_by(self, key_type, cumulative):
         if key_type not in ('traceback', 'filename', 'lineno'):
             raise ValueError("unknown key_type: %r" % (key_type,))
         if cumulative and key_type not in ('lineno', 'filename'):
-            raise ValueError("cumulative mode cannot by used "
+            raise ValueError("cumulative mode cannot be used "
                              "with key type %r" % key_type)
 
         stats = {}