json module should issue warning about duplicate keys

GitHub fields:

assignee = 'https://github.com/etrepum'
closed_at = None
created_at = <Date 2021-08-31.00:30:37.913>
labels = ['type-feature', 'library', '3.11']
title = 'json module should issue warning about duplicate keys'
updated_at = <Date 2021-11-14.01:49:22.181>
user = 'https://github.com/Zeturic'

bugs.python.org fields:

activity = <Date 2021-11-14.01:49:22.181>
actor = 'rhettinger'
assignee = 'bob.ippolito'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-08-31.00:30:37.913>
creator = 'Zeturic'
dependencies = []
files = []
hgrepos = []
issue_num = 45054
keywords = []
message_count = 5.0
messages = ['400678', '400696', '406181', '406182', '406302']
nosy_count = 5.0
nosy_names = ['rhettinger', 'bob.ippolito', 'corona10', 'Zeturic', 'andrei.avk']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue45054'
versions = ['Python 3.11']