Update version to 2.41.0-pre1 (on the release branch)

[jtattermusch]

I will publish the pre-release right after merging this. Let me know if there's any blockers.

[JamesNK]

btw the reason for the failing tests is this line:

grpc-dotnet/test/Grpc.Net.Client.Tests/AsyncUnaryCallTests.cs

Line 87 in 530eb1c

Assert.IsTrue(grpcVersion.Product!.Version!.Length <= 10);

The version is one character too long: 2.41.0-pre1

Change it to Assert.IsTrue(grpcVersion.Product!.Version!.Length <= 11);

I'm not sure why this hasn't failed before when the product name goes from 2.41.0-dev to 2.41.0-pre1. Something related to the user-agent string update?

[JamesNK]

The gRPC package version needs to be updated to 2.41.0?

grpc-dotnet/build/dependencies.props

Line 6 in 530eb1c

<GrpcPackageVersion>2.40.0</GrpcPackageVersion>

[jtattermusch]

Test failure should be fixed by #1486

[JamesNK]

Needs rebase, then it should pass.

[jtattermusch]

@JamesNK I just pushed the nuget packages and created a release:
https://github.com/grpc/grpc-dotnet/releases/tag/v2.41.0-pre1
(and btw the new "autogenerate release notes" feature didn't seem to generate meaningful contents, so I left the release notes empty for now and they'll need to be filled in by hand).