Update to net5.0 using a fix for net5.0 support in dotnetcore.yml

- Update actions/checkout to v2.
- setup-dotnet requires specific version or a wildcard so I changed it to 5.0.x so it targets any 5.0 version.
- Updated Raylib-cs.Tests to target net5.0 as we can now use it properly.

.github/workflows/dotnetcore.yml

@@ -1,5 +1,4 @@
 name: .NET Core
-
 on:
   push:
   pull_request:
@@ -12,12 +11,11 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest, macOS-latest]
-
     steps:
-      - uses: actions/checkout@v1
-      - name: Setup .NET Core
+      - uses: actions/checkout@v2
+      - name: Setup dotnet
         uses: actions/setup-dotnet@v1
         with:
-          dotnet-version: 3.1.100
+          dotnet-version: 5.0.x
       - name: Build with dotnet
         run: dotnet build -c Release

Raylib-cs.Tests/Raylib-cs.Tests.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net5.0</TargetFrameworks>
     <Platforms>AnyCPU</Platforms>
     <Configurations>Debug;Release</Configurations>
   </PropertyGroup>