Let us use C# 9 (restsharp#1609)

* Let us use C# 9

* Make the build happy

Author: alexeyzimarev

.github/workflows/build-dev.yml

@@ -12,18 +12,6 @@ on:
       - '*'
 
 jobs:
-#  test-netcore-linux:
-#    runs-on: ubuntu-latest
-#
-#    steps:
-#      - uses: actions/[email protected]
-#      - uses: actions/setup-dotnet@v1
-#        with:
-#          dotnet-version: '3.1.201'
-#
-#      - name: Run tests netcoreapp3.1
-#        run: dotnet test -c Release -f netcoreapp3.1
-
   test-win:
     runs-on: windows-latest
 

.github/workflows/pull-request.yml

@@ -10,7 +10,7 @@ jobs:
       - uses: actions/[email protected]
       - uses: actions/[email protected]
         with:
-          dotnet-version: '3.1.201'
+          dotnet-version: '5.0'
 
       - name: Run tests
         run: dotnet test -c Release

benchmarks/RestSharp.Benchmarks/RestSharp.Benchmarks.csproj

@@ -2,7 +2,7 @@
 
     <PropertyGroup>
         <OutputType>Exe</OutputType>
-        <TargetFramework>netcoreapp3.1</TargetFramework>
+        <TargetFramework>net5</TargetFramework>
     </PropertyGroup>
 
     <ItemGroup>

test/RestSharp.IntegrationTests/RestSharp.IntegrationTests.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net452;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net452;net5</TargetFrameworks>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(TargetFramework)|$(Platform)'=='Debug|net452|AnyCPU'">
     <WarningLevel>0</WarningLevel>

test/RestSharp.Serializers.Tests/RestSharp.Serializers.Tests.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net461;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net461;net5</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>

test/RestSharp.Tests.Shared/RestSharp.Tests.Shared.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net452;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net452;net5</TargetFrameworks>
     <IsTestProject>false</IsTestProject>
   </PropertyGroup>
   <ItemGroup>

test/RestSharp.Tests/RestSharp.Tests.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net452;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net452;net5</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Moq" Version="4.16.1" />