Testtools has some problems in the CI

Job #114945 failed for a472b36f:

I am trying to use dune-testools to perform system test on the CI. The problem comes specifically on the pip install pyparsing call made by dune-testtools:

-- Installing python package at /builds/santiago.ospina/dune-copasi/source/dune-testtools/python into the virtualenv...
CMake Error at /builds/santiago.ospina/dune-copasi/source/dune-common/cmake/modules/DuneExecuteProcess.cmake:44 (message):
  dune_python_install_package: Error installing into virtualenv!

  Run
  command:/builds/santiago.ospina/dune-copasi/build/dune-python-venv/bin/python;-m;pip;install;--upgrade;/builds/santiago.ospina/dune-copasi/source/dune-testtools/python


  Return code: 1

  Detailed log:

  Processing /builds/santiago.ospina/dune-copasi/source/dune-testtools/python

  Collecting pyparsing>=2.1.10 (from dune.testtools==2.4)

    Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', OSError('Tunnel connection failed: 403 Forbidden'))': /simple/pyparsing/
    Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', OSError('Tunnel connection failed: 403 Forbidden'))': /simple/pyparsing/
    Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', OSError('Tunnel connection failed: 403 Forbidden'))': /simple/pyparsing/
    Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', OSError('Tunnel connection failed: 403 Forbidden'))': /simple/pyparsing/
    Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', OSError('Tunnel connection failed: 403 Forbidden'))': /simple/pyparsing/
    Could not find a version that satisfies the requirement pyparsing>=2.1.10 (from dune.testtools==2.4) (from versions: )

  No matching distribution found for pyparsing>=2.1.10 (from
  dune.testtools==2.4)

I checked the dune-testtools CI and I coundl't find any obvios difference between their configuration and mine.