Code coverage report seems wrong on 3.8

# Summary



Running the same tests with nox against Python 3.6, 3.7 and 3.8 shows wrong report being generated for Python 3.8. This seems to be caused by the fact that the number of reported lines for some sources is wrong.



## Expected vs actual result



The report generated with Python 3.6 seems fine:

~~~

----------- coverage: platform linux, python 3.6.9-final-0 -----------

Name                          Stmts   Miss  Cover   Missing

-----------------------------------------------------------

austin/__init__.py               60     15    75%   86-87, 92-99, 114, 122, 134, 155, 165, 182

austin/aio.py                    32      2    94%   84, 107

austin/cli.py                    63      2    97%   160, 171

austin/format/__init__.py         0      0   100%

austin/format/speedscope.py      75     17    77%   112, 119, 160-197, 201

austin/simple.py                 29      2    93%   72, 93

austin/stats.py                 122      3    98%   223, 255, 273

austin/threads.py                17      2    88%   81, 93

-----------------------------------------------------------

TOTAL                           398     43    89%

~~~



This is what the same tests produce with Python 3.8

~~~

----------- coverage: platform linux, python 3.8.3-final-0 -----------

Name                          Stmts   Miss  Cover   Missing

-----------------------------------------------------------

austin/__init__.py               74     42    43%   86-87, 92-122, 134, 155-1447

austin/aio.py                    44     35    20%   329-1657

austin/cli.py                   126     93    26%   160-171, 306-2957

austin/format/__init__.py         0      0   100%

austin/format/speedscope.py     113     71    37%   160-1477

austin/simple.py                 34     25    26%   319-866

austin/stats.py                 132      9    93%   223, 255, 273, 329-691

austin/threads.py                17      2    88%   81, 93

-----------------------------------------------------------

TOTAL                           540    277    49%

~~~



Note how some sources in the 3.8 case are reported to be ridiculously larger than in the 3.6 case.



# Reproducer



It seems to happen with every test run.



## Versions



pytest (5.4.2)

pytest-cov (2.9.0)

nox (2020.5.24)



## Config



Please ask me in a comment if you need anything in particular.



## Code



Currently from a private repository

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