Build using .NET 6.0.300 public (#2031)

scripts/azure-pipelines-variables.yml

@@ -14,7 +14,7 @@ variables:
   MONO_VERSION_LINUX: ''
   XCODE_VERSION: 13.2.1
   VISUAL_STUDIO_VERSION: '17/pre'
-  DOTNET_VERSION_PREVIEW: '6.0.300-preview.22207.16'
+  DOTNET_VERSION_PREVIEW: ''
   DOTNET_WORKLOAD_SOURCE: 'https://aka.ms/dotnet/maui/6.0.300/rc.3.json'
   CONFIGURATION: 'Release'
   DOTNET_SKIP_FIRST_TIME_EXPERIENCE: true