EnvBuilder.install_scripts should use explicit permissions

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-10-02.18:57:46.948>
labels = ['3.8', 'type-bug', '3.7', '3.9', '3.10']
title = 'EnvBuilder.install_scripts should use explicit permissions'
updated_at = <Date 2020-10-03.01:10:11.726>
user = 'https://github.com/FRidh'

bugs.python.org fields:

activity = <Date 2020-10-03.01:10:11.726>
actor = 'jherland'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2020-10-02.18:57:46.948>
creator = 'Frederik Rietdijk'
dependencies = []
files = []
hgrepos = []
issue_num = 41913
keywords = []
message_count = 2.0
messages = ['377828', '377829']
nosy_count = 2.0
nosy_names = ['Frederik Rietdijk', 'jherland']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue41913'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9', 'Python 3.10']