explicitly exclude protobuf 4.21.0

Author: parthea

setup.py

@@ -35,7 +35,7 @@
     "google-cloud-core >= 2.0.0, <3.0.0dev",
     "grpc-google-iam-v1 >=0.12.4, <1.0.0dev",
     "proto-plus >= 1.22.0, <2.0.0dev",
-    "protobuf>=3.19.5,<5.0.0dev,!=3.20.0,!=3.20.1,!=4.21.1,!=4.21.2,!=4.21.3,!=4.21.4,!=4.21.5",
+    "protobuf>=3.19.5,<5.0.0dev,!=3.20.0,!=3.20.1,!=4.21.0,!=4.21.1,!=4.21.2,!=4.21.3,!=4.21.4,!=4.21.5",
 ]
 extras = {}