duplicate-code error only shows up with pylint-jobs=1

[jpsamper2009]

Steps to reproduce

$ git clone https://gitlab.com/apexai/grge
$ cd grge
$ git checkout 98188d88df1c6b5febf9f78a8bd8f969e2d158a1
$ python3.7 -m venv venv
$ source venv/bin/activate
$ pip install -r requirements/tests.txt
$ pytest --pylint -m pylint --pylint-jobs=1
...
1 failed, 32 passed
$ rm -rf .pytest_cache
$ pytest --pylint -m pylint
...
33 passed

Current behavior

• We get a duplicate-code error when we run pylint in a single thread, but not when running on multiple threads

Expected behavior

• We get a duplicate-code error regardless of the number of pylint jobs

pylint --version output

$ pylint --version
pylint 2.3.1
astroid 2.2.5
Python 3.7.5 (default, Nov  1 2019, 02:16:38) 
[Clang 10.0.0 (clang-1000.11.45.5)]

[doublethefish]

Also see #374

[Pierre-Sassoulas]

Should be fixed by #4007, (that is #3458 rebased on the latest code).