Measuring coverage in python threads

I am trying to measure code coverage with a code that uses threads created by the python threading module. I am using coverage to measure coverage. However I can not get the code that is run within a thread to get measured. I tried following the suggestion on the coverage docs to measure coverage in subprocesses but no luck.

Here is a minimal example file untitled.py:

import time, threading
import numpy as np


def thread():
    print(f'{threading.get_ident()}: started thread')
    time.sleep(np.random.uniform(1, 10))
    print(f'{threading.get_ident()}: done')

    
def run_threads():
    threads = [threading.Thread(target=thread)]
    for t in threads:
        t.start()
        
    print('started all threads')
        
    for t in threads:
        t.join()
        
    print('all threads done')


if __name__ == '__main__':
    
    run_threads()

> coverage run untitled.py
139952541644544: started thread
started all threads
139952541644544: done
all threads done
> coverage combine
Combined data file .coverage.248973.677959
> coverage report -m
Name          Stmts   Miss  Cover   Missing
-------------------------------------------
untitled.py      14      3    79%   6-8
-------------------------------------------
TOTAL            14      3    79%
> 

As you can see the lines 6-8 (the thread() function) is executed but not measured.

For context I am running on a linux machine, Python 3.9.0, coverage 6.2. The directory contains this .coveragerc file:

# .coveragerc to control coverage.py
[run]
source = ./
parallel = True
concurrency = multiprocessing

[report]
# Regexes for lines to exclude from consideration
exclude_lines =
    # Have to re-enable the standard pragma
    pragma: no cover

    # Don't complain about missing debug-only code:
    def __repr__
    if self\.debug

    # Don't complain if tests don't hit defensive assertion code:
    raise AssertionError
    raise NotImplementedError

    # Don't complain if non-runnable code isn't run:
    if 0:
    if __name__ == .__main__.:

I am very thankful for any suggestion!!