use pip for pytest and pytest plugins on macos

Author: simonjayhawkins

ci/deps/azure-macos-35.yaml

@@ -21,10 +21,10 @@ dependencies:
  - xlrd
  - xlsxwriter
  - xlwt
- # universal
- - pytest>=4.0.2
- - pytest-xdist
- - pytest-mock
  - pip:
  - python-dateutil==2.5.3
+ # universal
+ - pytest>=4.0.2
+ - pytest-xdist
+ - pytest-mock
  - hypothesis>=3.58.0