Prevent 'invalid escape sequence' errors in newer Python versions

[MrSerth]

Description of the change

This PR changes two additional occurrences of RegEx character classes to work with upcoming Python versions

Benefits

The existing code continues to work with Python 3.12+. Otherwise, the following error is returned:

/sbin/my_init:25: SyntaxWarning: invalid escape sequence '\W'
  SHENV_NAME_WHITELIST_REGEX = re.compile('\W')
/sbin/my_init:96: SyntaxWarning: invalid escape sequence '\Z'
  value = re.sub('\n\Z', '', f.read())

Possible drawbacks

None, backward compatible change.

Applicable issues

None

Additional information

None