chore: Update templates for .net9 and make .net9 default

Author: linkdotnet

src/bunit.template/template/.template.config/template.json

@@ -82,7 +82,7 @@
 			"description": "The target framework sdk for the project.",
 			"displayName": "Target framework sdk",
 			"datatype": "choice",
-			"defaultValue": "net7.0",
+			"defaultValue": "net9.0",
 			"replaces": "targetSdk",
 			"choices": [
 				{
@@ -99,6 +99,11 @@
 					"choice": "net8.0",
 					"description": ".net 8.0",
 					"displayName": ".net 8.0"
+				},
+				{
+					"choice": "net9.0",
+					"description": ".net 9.0",
+					"displayName": ".net 9.0"
 				}
 			]
 		}