Grpc.Tools signals libprotobuf warnings as errors

[codami]

What version of gRPC and what language are you using?

C#
Google.Protobuf: 3.18.0
Grpc.AspNetCore: 2.39.0
Grpc.Tools: 2.40.0

What operating system (Linux, Windows,...) and version?

Linux & Windows

What did you do?

I was building a .NET Class Library (gRPC Server side code) out of a proto file, using "dotnet build" and the _Protobuf_CoreCompile task failed after a couple of errors like this one:
[libprotobuf WARNING T : error : \src\github\grpc\workspace_protoc_windows_x64\third_party\protobuf\src\google\protobuf\compiler\csharp\csharp_enum.cc:74] Duplicate enum value Short (originally MY_VIEW_SHORT) in MyView; adding underscore to distinguish

What did you expect to see?

I would expect to see warnings at most, since the libprotobuf output was just a warning.

What did you see instead?

The build failed because of errors.

After starting the command manually I have noticed that the original output from the libprotobuf is this one:
[libprotobuf WARNING T:\src\github\grpc\workspace_protoc_windows_x64\third_party\protobuf\src\google\protobuf\compiler\csharp\csharp_enum.cc:74] Duplicate enum value Short (originally MY_VIEW_SHORT) in MyView; adding underscore to distinguish

A closer look at the Grpc.Tools implementation shows that the warning above is converted into error by this matching regex:

grpc/src/csharp/Grpc.Tools/ProtoCompile.cs

Line 214 in ab6beb3

pattern: "^(?'FILENAME'.+?): ?(?'TEXT'.*)",

[tonydnewell]

I've created a PR to fix this