Add .Net 7 (#853)

* Add .NET 7

* UseDotNet

* 7

* Ubuntu 6

* 'Use .NET 7'

* 67

* .

* use 7

* use 7

* test = 7

* coverage.7.0.opencover.xml

azure-pipelines-nuget.yml

@@ -12,6 +12,12 @@ steps:
     echo "BuildId = $(buildId)"
   displayName: 'Print buildId'
 
+- task: UseDotNet@2
+  displayName: 'Use .NET 7'
+  inputs:
+    packageType: sdk
+    version: 7.0.x
+
 # Based on https://whereslou.com/2018/09/versioning-and-publishing-nuget-packages-automatically-using-azure-devops-pipelines/
 - task: DotNetCoreCLI@2
   displayName: Build Release