Revert "Set Preview .NET version to 9.0 for main"

This reverts commit dff8fd8.

Author: pjcollins

tools/devops/automation/templates/variables/common.yml

@@ -68,4 +68,4 @@ variables:
   value: 9.0
 
 - name: DotNetPreviewSdkVersion
-  value: 9.0
+  value: 10.0