block py.test 3.9.1

references:

https://github.com/pytest-dev/pytest/issues/4181

Change-Id: I216fde19dd0f5c4910d76c08400f2329b09ad584
(cherry picked from commit b4d42a84e2)

setup.py

@@ -139,7 +139,7 @@ def run_setup(with_cext):
         package_dir={'': 'lib'},
         license="MIT License",
         cmdclass=cmdclass,
-        tests_require=['pytest >= 2.5.2', 'mock', 'pytest-xdist'],
+        tests_require=['pytest>=2.5.2,!=3.9.1', 'mock', 'pytest-xdist'],
         long_description=readme,
         classifiers=[
             "Development Status :: 5 - Production/Stable",
@@ -157,7 +157,7 @@ def run_setup(with_cext):
             'mysql': ['mysqlclient'],
             'pymysql': ['pymysql'],
             'postgresql': ['psycopg2'],
-            'postgresql_psycopg2binary': ['psycopg2-binary'],            
+            'postgresql_psycopg2binary': ['psycopg2-binary'],
             'postgresql_pg8000': ['pg8000'],
             'postgresql_psycopg2cffi': ['psycopg2cffi'],
             'oracle': ['cx_oracle'],

tox.ini

@@ -13,7 +13,7 @@ cov_args=--cov=sqlalchemy --cov-report term --cov-append --cov-report xml --excl
 usedevelop=
      cov: True
 
-deps=pytest
+deps=pytest!=3.9.1
      pytest-xdist
      mock
      # needed only for correct profiling results