commands: Enable format flag with hugo new site

Fixes #11155

testscripts/commands/new.txt

@@ -2,6 +2,8 @@
 
 hugo new site -h
 stdout 'Create a new site in the provided directory'
+hugo new site my-yaml-site --format yml
+checkfile my-yaml-site/hugo.yml
 hugo new site mysite -f
 stdout 'Congratulations! Your new Hugo site is created in'
 cd mysite
@@ -45,6 +47,3 @@ draft: true
 ---
 
 Dummy content.
-
-
-