fix(deps): require protobuf<4.0.0 on v1 branch

noxfile.py

@@ -42,7 +42,7 @@ def lint(session):
     Returns a failure if the linters find linting errors or sufficiently
     serious code quality issues.
     """
-    session.install("flake8", BLACK_VERSION)
+    session.install("flake8", BLACK_VERSION, "click<8.1")
     session.run("black", "--check", *BLACK_PATHS)
     session.run("flake8", "google", "tests")
 
@@ -52,12 +52,8 @@ def blacken(session):
     """Run black.
 
     Format code to uniform standard.
-
-    This currently uses Python 3.6 due to the automated Kokoro run of synthtool.
-    That run uses an image that doesn't have 3.6 installed. Before updating this
-    check the state of the `gcp_ubuntu_config` we use for that Kokoro run.
     """
-    session.install(BLACK_VERSION)
+    session.install(BLACK_VERSION, "click<8.1")
     session.run("black", *BLACK_PATHS)
 
 

setup.py

@@ -27,6 +27,7 @@
     "google-api-core[grpc] >= 1.31.5, <3.0.0dev,!=2.0.*,!=2.1.*,!=2.2.*,!=2.3.0",
     "grpc-google-iam-v1 >= 0.12.3, < 0.13dev",
     'enum34; python_version < "3.4"',
+    "protobuf<4.0.0dev",
 ]
 
 package_root = os.path.abspath(os.path.dirname(__file__))