Update build system to support .NET 3.1 and 5.0

Author: Arkatufus

build-system/azure-pipeline.template.yaml

@@ -16,6 +16,15 @@ jobs:
         clean: false  # whether to fetch clean each time
         submodules: recursive  # set to 'true' for a single level of submodules or 'recursive' to get submodules of submodules
         persistCredentials: true
+      - task: UseDotNet@2
+        displayName: 'Use .NET 5 SDK 5.0.101'
+        inputs:
+          version: 5.0.101
+      - task: UseDotNet@2
+        displayName: 'Use .NET Core Runtime 3.1.10'
+        inputs:
+          packageType: runtime
+          version: 3.1.10
       # Linux or macOS
       - task: Bash@3 
         displayName: Linux / OSX Build