Pin virtualenv to 16.7.10 (#10853)

virtualenv 16.7.11 appears to have broken our CI by upgrading the
version of pip embedded to something that doesn't support python 2, so
this pins virtualenv to the last version that we know works.

Author: pranavrajpal

.github/workflows/test.yml

@@ -40,7 +40,7 @@ jobs:
         python-version: ${{ matrix.python }}
         architecture: ${{ matrix.arch }}
     - name: install tox
-      run: pip install --upgrade 'setuptools!=50' 'virtualenv<20' tox==3.20.1
+      run: pip install --upgrade 'setuptools!=50' 'virtualenv<16.7.11' tox==3.20.1
     - name: setup tox environment
       run: tox -e ${{ matrix.toxenv }} --notest
     - name: test

.travis.yml

@@ -85,7 +85,7 @@ jobs:
 install:
 # pip 21.0 no longer works on Python 3.5
 - pip install -U pip==20.3.4 setuptools
-- pip install -U 'virtualenv<20'
+- pip install -U 'virtualenv<16.7.11'
 - pip install -U tox==3.20.1
 - python2 -m pip install --user -U typing
 - tox --notest

test-requirements.txt

@@ -12,6 +12,6 @@ pytest-forked>=1.3.0,<2.0.0
 pytest-cov>=2.10.0,<3.0.0
 typing>=3.5.2; python_version < '3.5'
 py>=1.5.2
-virtualenv<20
+virtualenv<16.7.11
 setuptools!=50
 importlib-metadata==0.20