.NET9.0, update Microsoft.AspNet.WebApi.Client to 6.0.0

I remove the tests for ConcurrencyTest. The module was not actually
used in normal build pipeline and i used and old (pre .net5) method for
parallelism and control of max connections in HttpClient. This
does not work any more. I just delete it.

Author: eivinhb

.github/workflows/build.yml

@@ -12,7 +12,7 @@ jobs:
     - name: Setup .NET
       uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: 8.x
+        dotnet-version: 9.x
     - name: Print openssl version
       run: |
         openssl version

.github/workflows/release.yml

@@ -13,7 +13,7 @@ jobs:
       - name: Setup .NET
         uses: actions/setup-dotnet@v4
         with:
-          dotnet-version: 8.x
+          dotnet-version: 9.x
       - name: Print openssl version
         run: |
           openssl version

Digipost.Api.Client.Archive.Tests/Digipost.Api.Client.Archive.Tests.csproj

@@ -3,7 +3,7 @@
     <PropertyGroup>
         <SignAssembly>true</SignAssembly>
         <AssemblyOriginatorKeyFile>..\signingkey.snk</AssemblyOriginatorKeyFile>
-        <TargetFramework>net8.0</TargetFramework>
+        <TargetFramework>net9.0</TargetFramework>
         <RootNamespace>Digipost.Api.Client.Archive.Tests</RootNamespace>
         <AssemblyName>Digipost.Api.Client.Archive.Tests</AssemblyName>
         <ProjectGuid>{c22f80a7-08e5-4836-9e24-e7bb431e9a5d}</ProjectGuid>

Digipost.Api.Client.Common.Tests/Digipost.Api.Client.Common.Tests.csproj

@@ -3,7 +3,7 @@
     <PropertyGroup>
         <SignAssembly>true</SignAssembly>
         <AssemblyOriginatorKeyFile>..\signingkey.snk</AssemblyOriginatorKeyFile>
-        <TargetFramework>net8.0</TargetFramework>
+        <TargetFramework>net9.0</TargetFramework>
         <RootNamespace>Digipost.Api.Client.Common.Tests</RootNamespace>
         <AssemblyName>Digipost.Api.Client.Common.Tests</AssemblyName>
         <ProjectGuid>{BC85F48B-9584-41F7-BBE8-EBBEC1EEC7E8}</ProjectGuid>