[3.9] bpo-33660: Fix PosixPath to resolve a relative path on root

[miss-islington]

(cherry picked from commit 94ad6c6)

Co-authored-by: Dong-hee Na donghee.na92@gmail.com

https://bugs.python.org/issue33660

[bedevere-bot]

@ambv: Please replace # with GH- in the commit message next time. Thanks!

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot x86 Gentoo Installed with X 3.9 has failed when building commit 211e4c6.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/527/builds/6) and take a look at the build logs.
4. Check if the failure is related to this commit (211e4c6) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/527/builds/6

Failed tests:

• test_smtpnet

Failed subtests:

• test_connect_using_sslcontext_verified - test.test_smtpnet.SmtpSSLTest
• test_connect_default_port - test.test_smtpnet.SmtpSSLTest

Summary of the results of the build (if available):

== Tests result: FAILURE then FAILURE ==

411 tests OK.

1 test failed:
test_smtpnet

13 tests skipped:
test_asdl_parser test_check_c_globals test_clinic test_devpoll
test_gdb test_ioctl test_kqueue test_msilib test_startfile
test_winconsoleio test_winreg test_winsound test_zipfile64

1 re-run test:
test_smtpnet

Total duration: 42 min 32 sec

Click to see traceback logs

Traceback (most recent call last):
  File "/buildbot/buildarea/cpython/3.9.ware-gentoo-x86.installed/build/target/lib/python3.9/test/test_smtpnet.py", line 82, in test_connect_using_sslcontext_verified
    server = smtplib.SMTP_SSL(self.testServer, self.remotePort, context=context)
  File "/buildbot/buildarea/cpython/3.9.ware-gentoo-x86.installed/build/target/lib/python3.9/smtplib.py", line 1034, in __init__
    SMTP.__init__(self, host, port, local_hostname, timeout,
  File "/buildbot/buildarea/cpython/3.9.ware-gentoo-x86.installed/build/target/lib/python3.9/smtplib.py", line 253, in __init__
    (code, msg) = self.connect(host, port)
  File "/buildbot/buildarea/cpython/3.9.ware-gentoo-x86.installed/build/target/lib/python3.9/smtplib.py", line 341, in connect
    (code, msg) = self.getreply()
  File "/buildbot/buildarea/cpython/3.9.ware-gentoo-x86.installed/build/target/lib/python3.9/smtplib.py", line 398, in getreply
    raise SMTPServerDisconnected("Connection unexpectedly closed")
smtplib.SMTPServerDisconnected: Connection unexpectedly closed


Traceback (most recent call last):
  File "/buildbot/buildarea/cpython/3.9.ware-gentoo-x86.installed/build/target/lib/python3.9/test/test_smtpnet.py", line 59, in test_connect_default_port
    server = smtplib.SMTP_SSL(self.testServer)
  File "/buildbot/buildarea/cpython/3.9.ware-gentoo-x86.installed/build/target/lib/python3.9/smtplib.py", line 1034, in __init__
    SMTP.__init__(self, host, port, local_hostname, timeout,
  File "/buildbot/buildarea/cpython/3.9.ware-gentoo-x86.installed/build/target/lib/python3.9/smtplib.py", line 253, in __init__
    (code, msg) = self.connect(host, port)
  File "/buildbot/buildarea/cpython/3.9.ware-gentoo-x86.installed/build/target/lib/python3.9/smtplib.py", line 341, in connect
    (code, msg) = self.getreply()
  File "/buildbot/buildarea/cpython/3.9.ware-gentoo-x86.installed/build/target/lib/python3.9/smtplib.py", line 398, in getreply
    raise SMTPServerDisconnected("Connection unexpectedly closed")
smtplib.SMTPServerDisconnected: Connection unexpectedly closed