pymalloc should align to max_align_t

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2022-03-31.08:59:44.707>
labels = ['expert-C-API']
title = 'pymalloc should align to max_align_t'
updated_at = <Date 2022-04-07.19:36:04.980>
user = 'https://github.com/encukou'

bugs.python.org fields:

activity = <Date 2022-04-07.19:36:04.980>
actor = 'ronaldoussoren'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['C API']
creation = <Date 2022-03-31.08:59:44.707>
creator = 'petr.viktorin'
dependencies = []
files = []
hgrepos = []
issue_num = 47179
keywords = []
message_count = 5.0
messages = ['416421', '416433', '416434', '416435', '416939']
nosy_count = 5.0
nosy_names = ['ronaldoussoren', 'pitrou', 'vstinner', 'petr.viktorin', 'methane']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue47179'
versions = []