pydoc: Use of MANPAGER variable is incorrect

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-01-20.21:02:23.588>
labels = ['type-feature', 'library', '3.9']
title = 'pydoc: Use of MANPAGER variable is incorrect'
updated_at = <Date 2020-02-03.18:34:42.431>
user = 'https://github.com/RPigott'

bugs.python.org fields:

activity = <Date 2020-02-03.18:34:42.431>
actor = 'Brocellous'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-01-20.21:02:23.588>
creator = 'Brocellous'
dependencies = []
files = []
hgrepos = []
issue_num = 39400
keywords = ['patch']
message_count = 3.0
messages = ['360332', '360336', '361318']
nosy_count = 2.0
nosy_names = ['serhiy.storchaka', 'Brocellous']
pr_nums = ['18123']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue39400'
versions = ['Python 3.9']