ci: Fix Python 2.7 builds on macOS 11

With current macOS 11 images tox is run under Python 3.12 and setuptools
isn't installed by default. E.g.

```
python -mtox -e "py27-mode_localhost-ansible4"
========================== Starting Command Output ===========================
/bin/bash --noprofile --norc /Users/runner/work/_temp/93a29c4c-f606-45e4-8dbd-a4a5f51b8730.sh
GLOB sdist-make: /Users/runner/work/1/s/setup.py
ERROR: invocation failed (exit code 1), logfile: /Users/runner/work/1/s/.tox/log/GLOB-0.log
================================== log start ===================================
Traceback (most recent call last):
  File "/Users/runner/work/1/s/setup.py", line 32, in <module>
    from setuptools import find_packages, setup
ModuleNotFoundError: No module named 'setuptools'
```

Installing setuptools under 3.12 chooses package versions incompatible with
Python 2.7.

.ci/azure-pipelines-steps.yml

@@ -24,7 +24,7 @@ steps:
   displayName: Install build deps
   condition: and(eq(variables['python.version'], ''), eq(variables['Agent.OS'], 'Linux'))
 
-- script: python -mpip install "tox<4.0"
+- script: python -mpip install "setuptools" "tox<4.0"
   displayName: Install tooling
 
 - script: python -mtox -e "$(tox.env)"

.ci/azure-pipelines.yml

@@ -20,23 +20,28 @@ jobs:
   strategy:
     matrix:
       Mito_27:
+        python.version: '2.7'
         tox.env: py27-mode_mitogen
       Mito_311:
         python.version: '3.11'
         tox.env: py311-mode_mitogen
 
       # TODO: test python3, python3 tests are broken
       Loc_27_210:
+        python.version: '2.7'
         tox.env: py27-mode_localhost-ansible2.10
       Loc_27_4:
+        python.version: '2.7'
         tox.env: py27-mode_localhost-ansible4
 
       # NOTE: this hangs when ran in Ubuntu 18.04
       Van_27_210:
+        python.version: '2.7'
         tox.env: py27-mode_localhost-ansible2.10
         STRATEGY: linear
         ANSIBLE_SKIP_TAGS: resource_intensive
       Van_27_4:
+        python.version: '2.7'
         tox.env: py27-mode_localhost-ansible4
         STRATEGY: linear
         ANSIBLE_SKIP_TAGS: resource_intensive