Upgrade Grpc.Core packages to 2.34.0-pre1 (#1130)

Author: jtattermusch

build/dependencies.props

@@ -3,7 +3,7 @@
     <BenchmarkDotNetPackageVersion>0.12.1</BenchmarkDotNetPackageVersion>
     <GoogleProtobufPackageVersion>3.14.0</GoogleProtobufPackageVersion>
     <GrpcDotNetPackageVersion>2.33.1</GrpcDotNetPackageVersion>  <!-- Used by example projects -->
-    <GrpcPackageVersion>2.33.1</GrpcPackageVersion>
+    <GrpcPackageVersion>2.34.0-pre1</GrpcPackageVersion>
     <MicrosoftAspNetCoreAppPackageVersion>5.0.0</MicrosoftAspNetCoreAppPackageVersion>
     <MicrosoftAspNetCoreApp31PackageVersion>3.1.3</MicrosoftAspNetCoreApp31PackageVersion>
     <MicrosoftBuildLocatorPackageVersion>1.2.2</MicrosoftBuildLocatorPackageVersion>