Update version to 2.33.1 (on v2.33.x branch) (#1095)

Author: jtattermusch

build/version.props

@@ -2,7 +2,7 @@
   <PropertyGroup>
 
     <!-- package version of grpc-dotnet -->
-    <GrpcDotnetVersion>2.33.1-pre1</GrpcDotnetVersion>
+    <GrpcDotnetVersion>2.33.1</GrpcDotnetVersion>
 
     <!-- assembly version of grpc-dotnet -->
     <GrpcDotnetAssemblyVersion>2.0.0.0</GrpcDotnetAssemblyVersion>