explicitly exclude protobuf 4.20.0

Author: parthea

setup.py

@@ -48,7 +48,7 @@
     install_requires=(
         "google-api-core[grpc] >= 1.32.0, <3.0.0dev,!=2.0.*,!=2.1.*,!=2.2.*,!=2.3.*,!=2.4.*,!=2.5.*,!=2.6.*,!=2.7.*",
         "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",
     ),
     python_requires=">=3.7",
     classifiers=[