security: Update Grpc.Net.Client library to address Dependabot alerts. (#1768) (#1769)

Author: chynesNR

src/Agent/NewRelic/Agent/Core/Core.csproj

@@ -66,7 +66,7 @@
 
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <!-- .NET Core can use the modern gRPC library -->
-    <PackageReference Include="Grpc.Net.Client" Version="2.51.0" />
+    <PackageReference Include="Grpc.Net.Client" Version="2.55.0" />
     <PackageReference Include="Autofac" Version="4.5.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration" Version="2.0.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Abstractions" Version="2.0.0" />