Remove protobuf 4.22.0 from testing (#32442)

This version broke backward compatibility in `plugin_pb2.py`, which is
presumably a relatively minor regression, since we have not yet heard
any complaints about it. This PR:

- Excludes `4.22.0` from installation
- _Includes_ protobuf pre-releases into testing so this can be caught
more quickly in the future.

When bad prereleases are caught, we can exclude them from testing in a
similar manner to this PR. We may eventually want to invest into a
system where we can define these bad versions centrally.

src/python/grpcio_tests/setup.py

@@ -42,8 +42,8 @@ INSTALL_REQUIRES = (
     'grpcio-status>={version}'.format(version=grpc_version.VERSION),
     'grpcio-tools>={version}'.format(version=grpc_version.VERSION),
     'grpcio-health-checking>={version}'.format(version=grpc_version.VERSION),
-    'oauth2client>=1.4.7', 'protobuf>=4.21.6', 'google-auth>=1.17.2',
-    'requests>=2.14.2')
+    'oauth2client>=1.4.7', 'protobuf>=4.21.6rc1,!=4.22.0.*',
+    'google-auth>=1.17.2', 'requests>=2.14.2')
 
 COMMAND_CLASS = {
     # Run `preprocess` *before* doing any packaging!

tools/run_tests/helper_scripts/build_python.sh

@@ -165,7 +165,7 @@ pip_install_dir_and_deps() {
 pip_install -U gevent
 
 pip_install --upgrade cython
-pip_install --upgrade six protobuf>=4.21.3
+pip_install --upgrade six 'protobuf>=4.21.3rc1,!=4.22.0.*'
 
 if [ "$("$VENV_PYTHON" -c "import sys; print(sys.version_info[0])")" == "2" ]
 then