remove virtualenv<20 constraint

.azure-pipelines/steps/install-dependencies.yml

@@ -16,7 +16,6 @@ steps:
     git submodule sync
     git submodule update --init --recursive
     $(PY_EXE) -m pip install --upgrade --upgrade-strategy=eager pip setuptools wheel
-    $(PY_EXE) -m pip install "virtualenv<20"
   env:
     PIPENV_DEFAULT_PYTHON_VERSION: ${{ parameters.python_version }}
     PYTHONWARNINGS: 'ignore:DEPRECATION'

.github/workflows/ci.yaml

@@ -67,7 +67,6 @@ jobs:
       run: |
         git submodule sync
         git submodule update --init --recursive
-        python -m pip install "virtualenv<20"
         python -m pip install -e . --upgrade
         pipenv install --deploy --dev --python=${{ steps.python-path.outputs.path }}
     - name: Run tests