Unclosed socket from luigi.rpc module

[starhel]

Description
Luigi does not close all connections to remote scheduler:

ResourceWarning: unclosed <socket.socket fd=10, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=(...), raddr=(...)>

This is probably connected to not closed requests.Session objects in RequestsFetcher.

luigi/luigi/rpc.py

Lines 100 to 118 in 78145d6

	class RequestsFetcher:
	def __init__(self, session):
	from requests import exceptions as requests_exceptions
	self.raises = requests_exceptions.RequestException
	self.session = session
	self.process_id = os.getpid()
	def check_pid(self):
	# if the process id change changed from when the session was created
	# a new session needs to be setup since requests isn't multiprocessing safe.
	if os.getpid() != self.process_id:
	self.session = requests.Session()
	self.process_id = os.getpid()
	def fetch(self, full_url, body, timeout):
	self.check_pid()
	resp = self.session.post(full_url, data=body, timeout=timeout)
	resp.raise_for_status()
	return resp.text

Packages

urllib3==1.26.9
requests==2.27.1
luigi==3.0.3 (same code on master)